TL;DR: Almost-certainly not
From the start, it is important to realize there is no recorded incidence of any new Crystal Sphere appearing since the beginning of the multiverse.¹ There is one cracked Crystal Sphere (the only known case of one being destroyed), and otherwise, as far as we know, all Crystal Spheres that exist have always existed; none were “created” after the fact.
It is possible that the aboleths or (more likely) leShay can remember a time prior to the existence of one or more Crystal Spheres, and therefore remember one or more coming into existence. If they have, this is not recorded in any canon source. Even in the unlikely event that they do remember this, they almost certainly do not know how this occurred. The aboleths, in particular, would probably have been opposed to it in the first place.
Anyway, creating a new Crystal Sphere would be really good for a lot of very powerful entities. Gods could create the Sphere tailored to their needs, allowing them to create a rich, reliable source of faith. Fiends could do likewise for souls; for that matter, so could celestials or any one else with such an interest.
Yet no one has ever done it, no matter how vast their resources. There is no canon source that suggests that anyone has the slightest inkling of how it could be done, or even solid evidence for or against it being possible at all. It may very well be that the Crystal Spheres came with the multiverse and to create more, you’d have to create a new multiverse.¹ Since multiverses do not tend to play nice with one another—see how the Far Realm interacts with ours for what tends to result from them coming into contact—you certainly couldn’t bring a Crystal Sphere over from your new multiverse back to this one even if you somehow managed to succeed on step 1.
- The novel Tymora’s Luck includes a strange passage in which the god Lathander describes newly-developing Crystal Spheres. He refers to this happening in “a new universe,” possibly confirming the thought that Crystal Spheres are only created at the beginning, but that’s very confusing because Lathander shouldn’t really have access to a new universe. Also, the new universe is described as “beyond the worlds of Tuhgri,” which is bizarre since you can’t put an entire universe just next to some planets, that doesn’t make any sense. (Also, “Tuhgri” doesn’t get mentioned anywhere else in D&D canon—that word is used in the Star Wars Expanded Universe, but that might just be coincidence.) Plus, it says “universe” rather than “multiverse,” which maybe means something but I don’t know what. Far greater experts in Planescape lore than I have basically just shrugged at this—no one really knows what it means. For this answer, I’m mostly ignoring it.
Your particular steps definitely do not create a “Crystal Sphere.” You are, at best, emulating a Crystal Sphere, not actually creating one.
But we can still go through your steps and determine how well each works, and evaluate how well the result mimics a Crystal Sphere.
Your Steps
- I've heard somewhere (source unclear) that through shear force of will: demiplanes can be created on the astral plane.
That is correct; the psionic power genesis has the effect of “A demiplane coterminous with the Astral Plane, centered on your location,” as opposed to the magical spell genesis, which has the effect of “A demiplane coterminous with the Ethereal Plane, centered on your location.” So a high-level manifester can create a demiplane on the Astral, while a high-level spellcaster can create a demiplane on the Ethereal. There isn’t much significantly different between the two, but it is a thing.
- Combining that with what Mr.Rrhexx says about the: "Astral being the place you are when you aren't anywhere ; the space between spaces ; where pocket dimensions expand to their full sizes & time does not flow actually it flows at infinitesimal value"
I don’t know anything about this Mr.Rrhexx, but I don’t love this definition of the Astral Plane. It’s got some poetic truth to it, but particularly the bit about not being anywhere, about space not being a thing in the Astral, that’s not accurate. The Astral Plane has its own concepts of space, direction, and distance, and you travel through it in much the same way you travel through other planes. There are definitely some oddities—subjective gravity, timelessness—but ultimately, the Astral is “the space between the planes,” that is, it exists in the gaps between various planes. It still has size, and though it doesn’t take “time” to move about in it—since it is timeless—there is still a sense that you are first in one place, and then later in another place, rather than being in all places at once.
It is more accurate to say that while you’re in the Astral, you treat all other planes as being on pause. With respect to other things in the Astral, time seems to move normally for you, aside from the speed with which spells may be cast.
Whether that “pause” is perfect or if time continues to move outside the Astral Plane at some “infinitesimal” rate is kind of philosophical, but I’m not aware of any source stating that.
- Combining that w/ my knowledge of the phlogiston, and The Living Sea, which shows that color pools can be inverted in rare cases and that phlogiston can't be brought into a crystal sphere and is its own spatial medium essentially between the shells containing wildspace, but would be not incapable of existing in the null space of the astral which is everywhere and nowhere and hence theoretically as indifferent to phlogiston as it is to the living water of the Living Sea.
I don’t believe there is anything here that contradicts this, though I think you’re imagining some greater significance here than there is.
Crystal Spheres are just generally impermeable—nothing goes through them except through the specific openings. Phlogiston isn’t “special” in this regard. The openings of Crystal Spheres do block phlogiston (while allowing other things), but since those are “portals,” that might not be special either.
That’s because phlogiston generally can’t interact with portals; planar connections just fail around the stuff. You can’t even communicate to another plane from within the phlogiston (or from another plane into the phlogiston). This prohibition is apparently absolute—not even gods can get around it. So you can’t take phlogiston off of the Material Plane to go “around” a Crystal Sphere. This same property likely is what prevents phlogiston from passing through the portals of a Crystal Sphere.
Anyway, most creatures never encounter phlogiston because they never visit the parts of the Material Plane that are outside of any Sphere. Those who do, use special ships known as spelljammers; this is the basis for the Spelljammer campaign setting, which hasn’t seen any love since 2e, so we can’t really state definitively anything about it in “3e or 5e canon.”
- Could enough psionics users working together in a psionic analog to epic magic...
That exists; see here.
Note that having “enough” epic manifesters doesn’t really matter—that’s only a question of whether or not you can get your Psicraft check high enough for whatever you want to do. I’m willing to stipulate that you can, whether it’s through an army of assistants or whatever other method, up to the limits that appear to be in place on the basis of “if that were possible, someone would have already done that, and no one has so it must not be possible.” Unfortunately, epic magic/psionics simply don’t have canonical limits, so that is going to be a somewhat subjective measure.
If you push your epic magic/psionics even harder, say, harder than anyone in the history of the multiverse has ever managed, even dozens of gods working in concert and applying all the force of their billions of worshippers, then we just can’t answer the question. Nothing says that epic magic/psionics can’t be pushed harder indefinitely. But at that point, there are literally zero limits of any kind, which makes this and any other question like it moot.
(except instead of dying at the end they'd just have to sync their minds at the beginning and may have to perform this ritual eternally for it to last eternally as far as I know)
I don’t really know what this is in reference to; maybe in 2e epic magic worked that way? 3e epic magic and psionics don’t cause the death of the spellcaster in most situations. That sounds more like someone was attempting to bite off a bigger epic spell than they could chew, and somehow leveraged their own life force to make it happen and pulled too hard.
- erect a barrier isolating themselves from the rest of the astral with a large array of gates cladded into a rough spherical formation (picture a Roman Sheild wall but 3D)...and then
The gate spell does not have a psionic analogue, and in any event gate specifies that it is circular. A circle cannot perfectly tessellate a surface; there will always be gaps or overlaps between the gates. It is not at all clear that overlaps are allowed, or what they would do if they happened. I imagine some “danger” à la bag of holding and a portable hold might occur here.
Forgotten Realms Campaign Setting does have Create Portal, which Player’s Guide to Faerûn ditches in favor of rolling that functionality into Craft Wondrous Item. These portals are “usually” circular, but other shapes are explicitly named, including some that can tessellate the approximate surface of a sphere. Both feats require spellcasting and caster level, rather than psionics, but there is a Magic Item Compendium rule that states that all magic item-creation feats and items have a psionic analogue. So when Player’s Guide to Faerûn says that you can create a portal with Craft Wondrous Item, Magic Item Compendium says you can do the same with Craft Universal Item. That’s the closest to a canonical answer that we have.
Note that both of those options are available without epic anything.
With respect to epic matters, none of the epic magic/psionics seeds directly claim to be responsible for creating a gate. One presumes, however, that some combination of the Conjure and Transport seeds could accomplish the creation of a portal. In reality, as I said, epic magic/psionics are wildly unbounded and therefore can do basically anything with DM approval; there is very, very little on its canonical limitations. We can only make arguments like those I made at the beginning of my answer that amount to “if it were possible, someone would have already done it.”
That argument probably doesn’t apply here, since there isn’t a lot of point to this maneuver—genesis already handles creating a separation for a demiplane from the rest of the Ethereal or Astral, and it’s not generally thought to be necessary to go beyond that. And if non-epic magic/psionics can do it, it certainly seems like epic magic/psionics ought to be able to.
But if you’re doing that, we can cut out some issues here and forget the whole “rough” part of this—epic magic/psionics can probably just make a spherical portal surface. For that matter, by the same argument, if non-epic magic/psionics can manage genesis, epic magic/psionics can probably just manage something much more grandiose from the get-go.
- make a plane analogous to phlogiston space through force of will, and then
If you mean, create a demiplane via genesis that is filled with phlogiston, maybe, but probably not, and even if you can, probably not perfectly.
To begin with, the psionic version of genesis specifies that it cannot create “esoteric material”—phlogiston definitely qualifies. The magic version of genesis doesn’t include that line, but since the magic version of genesis was written for 3e, and the psionic version is the only version to appear in the “v.3.5 revised edition,” the psionic version is the “official” version of the ability. The rules for updating from 3e to 3.5e would have the psionic version replace the older magic version entirely. Most groups elect to keep both, and maintain the Ethereal/Astral distinction between them, but even that much is technically beyond the official rules. It’s very, very likely that the updated rules for the psionic genesis should apply to the magic one—and that rules out phlogiston.
If you ignore that, and are using the old, magic version of genesis, technically, the only limitation is that you have to be able to visualize what your demiplane is going to be like. Phlogiston is fairly unique, colorful stuff, so visualizing it shouldn’t be hard for someone familiar with it. But phlogiston also has unique planar interference that likely prevents genesis from working the way it’s supposed to in this respect, even if we otherwise allow “esoteric material.” Instead, you’d probably get something that’s similar to, but not quite the same as phlogiston.
But for my money, genesis isn’t up to this task. Filling your demiplane with a phlogiston-like substance will have to be a task for a separate effort after you’re done creating the demiplane, and either way, you’re not getting “real” phlogiston.
If you mean plane rather than demiplane, then no, absolutely not. For the same reasons that we can be sure no one can create a new Crystal Sphere (if they could they would have), we likewise can be sure that no one can force the creation of a true, proper plane. New planes have happened—unlike new Crystal Spheres—including instances of demiplanes “growing up” into full planes, as with Shadow. But no one can control that process; it is a function of how the multiverse works and beyond the purview of even the greatest of gods.
You could maybe encourage it, by studying what has caused planes to develop in the past and then trying to engineer those circumstances, but you would not have precise control over the plane’s nature. For instance, it being filled with phlogiston is likely out, since there’s already a plane like that and the multiverse doesn’t really seem terribly enamored of redundancies like that. Even if you created it that way, it would likely lose that property when it became a proper plane—or just merge with the Material.
- will the space to allow psionics and sorcerers to cast spells at the same proficiency [as each other] via a weave that is maintained by a portion of the monk/psionic army...and then
This is the default and wouldn’t require “maintenance.” Spells and psionics function as normal on most planes, including the Astral, the Ethereal, and most demiplanes within them. You could probably create a demiplane that doesn’t allow these things if you really wanted, with extra effort, but the default is that they work.
Which is good, because there’s basically no evidence for it being possible to accomplish otherwise. (Monks, at least if we’re talking about the class, certainly have no ability to contribute to it.) We do have to talk here, a bit, about a divergence between 5e canon and prior canon. Before 5e, the Weave was unique to the Forgotten Realms—more helpfully, in this context, Realmspace. If someone from the Realms left that Crystal Sphere and went beyond Mystra’s (or Shar’s) influence, their magic continued to function without any problem because outside of that influence you never needed the Weave in the first place. If you visited the Realms from elsewhere, you had to start using the Weave, but it basically just “worked” unless you pissed Mystra off somehow. 5e changed that by saying that the Weave is everywhere—and never explained that at all. How it works, outside of Mystra’s (or Shar’s) influence, we just don’t know.
Either way, the canon on psionics in 3e was that manifesters basically project their own mini-Weave and that’s how psionics operates. And there are very limited abilities to use psionics to give others psionics—bestow power, metaconcert, psychic chirurgery—but nothing that grants spellcasting. It’s plausible for such a thing to exist—especially with epic psionics—but it’s not going to be a full, plane-wide Weave like we have in Realmspace. Not even Mystra or Shar can really create that—Mystra controls the Weave only because Ao gave it to her to do that, and Shar created the Shadow Weave out of the existing Weave, not wholecloth. Ao can dictate that Realmspace has a Weave and that control of it is the purview of one or more divine portfolios, as Ao is the overdeity for Realmspace, but while his power is nearly absolute within that Crystal Sphere, it’s nothing outside it.
- use move_earth combined with epic magic and either portals, or lots of supplies, make it into an unbreakable ceramic-like barrier which is some combination of dust particles combined with barrier spells and made so that it can't be naturally passed through except via portals, then semi-lastly
I mean, wall of force would be vastly simpler and much harder, but nothing you do is going to be immune to both disintegration and disjunction, to say nothing of epic magic/psionics and/or divine intervention.
Technically, you could do whatever “the Cube” did, but 1. what exactly that was has never been publicized, and has probably since been forgotten, and 2. the most likely hypothesis was that it involved an overclocked spell clock creating an absurd number of dispelling screens, which could be overwhelmed by a similarly-absurd number of disjunctions. Epic magic/psionics or divine intervention would likely make short work of that.
create another wall of gates facing the other way
(The first wall was to stop astral travelers from reaching your work space)
(the second wall is to connect your workspace to phlogiston space)
(Using world wide web analogies the first wall is like an online firewall and the second wall is a gateway to the web hosts making the demiplane analogous to a small public server and the phlogiston the anolog of the the world wide web with the astral being an analog of a parrallel world wide web and the space between the firewall and the netportal is like a private entranet with a psionic army working really hard to maintain balance and order)
OK, this is subject to the same discussion as the previous version, but I’m not really sure I’m following your analogy.
- use more more magics to create solid bodies, and a sun (vague on purpose not critical to answering the main question)
Genesis already does this for you, though you could certainly expand on what you get from that spell/power using additional spells.
The bigger problem is space to put it all. Genesis produces a demiplane 180 feet in diameter after a week worth of work, and you can expand that by 180 feet for every additional week of work you put in. Producing enough space to reach from the Sun to Earth, therefore, would take over 52 million years. Epic magic/psionics could plausibly speed up this process, plausibly by a considerable amount, but there is zero canonical definition for how that would work or how much you could speed things up. But even a factor of 1,000, which would be enormous, would only knock it down to 52,000 years.
The bigger problem is that demiplanes just don’t get this big. The largest canonical demiplane was the Demiplane of Shadow, which in 3e became a full Plane of Shadow. But we know very little about the extent of the demiplane version—all we’ve got is that it was the “largest.” As far as I’m aware, the largest demiplane left in 3e is the Demiplane of Dread, better known as Ravenloft. That’s got room for several nations in it, but several nations is a far cry from several planets and a star. The rules don’t specify any canonical limit on how large genesis can make things, but the reality of the setting certainly seems to imply that there is one.
The transition of the Demiplane of Shadow to the Plane of Shadow strongly suggests that at a certain size, your demiplane stops being your demiplane, and becomes a full plane—and it’s not “yours” anymore. See the discussion above.
- use illusion magic that has been amplified by either a portal or more psionics to be akin to shadow magic & illusions cast in the deep ethereal; to create gods to help with maintenance and act as self sustaining ethereal "quasi-constructs" for making everything run a bit smoother
Not sure why this would involve shadow magic, but in any event... no, probably not.
I mean, epic magic/psionics allows you to create other beings; the Conjure seed explicitly discusses how you can use it in combination with Life and Fortify to accomplish that. It explicitly mentions how you might give those beings powers; if you are powerful enough, that could include god-like powers. And beings with god-like powers might be prayed to, and the faithful might even receive prayers in response.
But you won’t be able to control divine portfolios. Even overdeities seem to have somewhat limited control over those; certainly no one else has any say in them. It is possible that the worship of these god-like artificial beings will result in those artificial beings developing divine portfolios, and becoming true gods, but you won’t control it—and you’ll lose much of your control over them. Gods are what they are believed to be—so unless you control the beliefs of the vast majority of the population, that might change these beings from what you wanted them to be. Even if you do, beliefs are often vague and nebulous, and gods have a fair amount of latitude in their behavior—and divine power allows them to do a lot with the wiggle room they’ve got. More importantly, it’s very unlikely that you’ll be able to prevent the development of problematic beliefs that may give rise to problematic gods, even if you keep the beliefs about your own artificial gods where you want them. Almost all planes belief in several gods that are literally dedicated to “being a problem,” in fact, which means the very absence of any repository for that sort of belief within your system is liable to cause the creation of a problematic god outside your system.
Basically, you’re trying to play overdeity here, without being one yourself, and you’re trying to achieve things that no overdeity has managed to do. Ao is one of the strictest overdeities known, and the gods of Realmspace have certainly caused many, many headaches for Ao. You want to do better than Ao with a fraction of Ao’s toolbox—that does not seem canonically plausible to me.
Conclusion
Yes, you can create your own demiplanes in the Astral, but filling it with phlogiston isn’t likely to happen. You can probably create something similar to phlogiston, though, and then you could probably embed something impervious to phlogiston within that plane, if you wanted, and create a world within that. An entire solar system, less likely—that would be a big demiplane. Big demiplanes do exist, so it might be just barely plausible, though I have serious doubts about creating two such fake-Crystal Spheres in the same demiplane.
Your fake-Crystal Sphere(s) will definitely remain just that, fakes, though with sufficiently powerful epic magic/psionics it might be hard to tell the difference—it’s plausible that you could create a substance that would require a more powerful epic mage/psion than yourself to break. Note, however, that many deities are likely going to qualify there, and that’s before we get into their actual divine abilities which are going to be intensely difficult to thwart without divine ability. It’s possible to become a deity yourself—more likely, really—but that comes with strings attached.
Speaking of “strings attached” to divine portfolios, that also applies to any fake-gods you attempt to create within your world. The more god-like they become, the greater the risk of them becoming actual gods—and that is likely to subvert them from your goals. Even the most powerful gods have difficulty controlling the portfolios of other gods, even the weakest. With carefully-engineered conditions and a sufficiently-isolated world, you could probably maintain it for a long, long time, but I wouldn’t bet on “indefinitely.” Sooner or later the issues are going to pile up beyond your ability to maintain the charade, even if that’s millions or billions of years hence.
For the best internet expertise in D&D cosmology from 3.5e and prior—that is, Planescape and Spelljammer, I suggest afroakuma’s Giant in the Playground threads.
