I am not focusing on “how do I best spend my enormous wealth?” since that’s much too broad for a question here; I am instead focusing on your requirements.
Sadly, for that we have to begin with this fact:
Crafting “All the Things” cannot be done
First, crafting “All the Things” is off the table. There is no way to do so in Paizo-published content. Items that do not replicate spells can have their spell requirements waived with an increase in DC, so the wondrous items you mention are fine, but scrolls cannot benefit from this. To produce a scroll, you must have the spell, period.
To get as many spells as possible, you could try to use mystic theurge, but you won’t succeed; you’ll be very far behind on both classes, and eventually you’ll run out of mystic theurge levels to take. If you could convince your DM to let you take a 14-level mystic theurge, and you’re starting at 20, you’d hit most things – but would still lack any spells not on those lists (say, druid spells if your divine side is cleric).
The other thing you could conceivably do is use items to make items, but that’s hardly from scratch: the first item had to come from someone who had the spell, and that won’t be you. Besides that, it’s pretty much pointless; a wand of whatever could make fifty scrolls of whatever but all that accomplished is turning your charges into more fragile, more difficult-to-use scrolls, at considerable cost and taking considerable time.
There are no good analogues to vitriolic spear
The attack you mention is clearly the warlock’s eldritch blast modified by vitriolic blast and quite probably eldritch spear. There are no good options that mimic this attack.
First of all, at-will magic is something Paizo apparently detests; their one example of it, the kineticist from Occult Adventures, is insultingly weak, and moreover it isn’t actually at-will: its abilities deal self-damage, and the kineticist is extremely limited in how much of that damage (called burn) they are allowed to take. The damage cannot be healed except by resting, so that basically becomes a per-day limit (and a tight one). There is a very counter-intuitive way to play kineticists in which you only use your 0-burn abilities; that’s basically at-will, and it works better than most kineticists, but it is still pretty terrible.
Secondly, mundanes aren’t doing a lot better here. While 3.5 had, for example, the gloves of endless javelins and the like, there are no options in Pathfinder for infinite ammunition, even plain old mundane ammunition. So a longbow isn’t a great analogue here, even if you can carry a lot of arrows. Talk to your DM about whether or not he tracks those, though: many don’t, and that could sort of be an answer.
Firearms are actually somewhat closer, kind of, to eldritch blast – like eldritch blast, they are a touch attack (and also like eldritch blast, their damage is difficult to improve). Unfortunately, the ammunition problems for longbows are dramatically worse with firearms: powder and bullets are very expensive, even for gunslingers who see massive discounts. Furthermore, firearms break very easily, making them painfully unreliable.
Closer to truly-infinite ranged attacks is a returning thrown weapon. This will come back to your hand at the start of your next turn (you have to be where you were when you threw it to catch it), eliminating the ammunition issue. If you have multiple attacks (and at 20th you have at least two), you need multiple returning weapons, or (much cheaper/more flexible) a blinkback belt though the latter works poorly unless you have Quick Draw. Quick Draw is close to required for a thrower anyway, though, so the blinkback belt is definitely the better play.
However, even that falls far short of vitriolic spear: most thrown weapons have very low range, you have to catch it, and most importantly, you need to hit real AC, not touch AC. That makes such weapons dramatically less reliable than vitriolic spear. You’re going to need better BAB, and quite likely better Dexterity, than you had as a warlock if you want to hit as frequently, and you’re also probably going to need to invest in your weapon, with feats (Far Shot) and magic (distance) to improve the range.
You can do some warlock-like things with ranged attacks though
The eldritch archer archetype for the magus is finally a ranged version of the magus that doesn’t suck, and magus is a fairly solid class for you. (Note that eldritch archer is quite new, and the list of archetypes on the magus page on the SRD hasn’t be updated to include. It is, in fact, a real thing, from Heroes of the Streets, and I’ve linked it since it can be difficult to find.)
The advantage of the magus is Spell Combat and Spellstrike. The former allows spellcasting in the middle of a full-attack, and the latter allows touch spells to be delivered with weapon attacks. The eldritch archer changes these to allow Spell Combat to be used with a ranged weapon and without a hand free (at the cost of the ability to improve Concentration checks), and using ranged weapons to deliver ranged touch attacks.
This means that an eldritch archer can deliver spells alongside a weapon attack. This seems very similar to the way Eldritch Essences were applied to the warlock’s eldritch blast, and goes a long way towards making your mundane weapon attack magical again.
Furthermore, the eldritch archer adds that returning property to the list of things that can be applied to weapons with Arcane Pool, along with distance and nimble shot (and at the cost of dancing, keen, and vorpal as options). Those definitely help in mitigating the problems associated with weapons that you did not have with eldritch blast.
So I recommend the eldritch archer here. The magus spell list is not going to be stellar at scroll scribing, but nothing is going to emulate Imbue Item in Pathfinder anyway. You can still be fine at crafting wondrous items.
The arcanist, on the other hand, is a wildly imbalanced and broken class. Seriously, I cannot more strongly recommend against inflicting that on your group.
At-will fly is not the same as constant flight: the headband of aerial agility +6 requires a standard action every 8 minutes to re-up the fly spell. It is again worth asking your DM if he’s going to be tracking this: it’s a headache for player and DM both, so the DM may simply waive it in favor of constant flight.
If not, and you want true, constant flight, wings of flying are 54,000 gp; cheaper than the headband, but no bonus to Intelligence. The maneuverability is also only average, but this means much less in Pathfinder than it did in 3.5. Being winged flight rather than just gravity-defiance is also a drawback (you can be tripped), and of course 54,000 gp is still vastly too much, but it’s what you’ve got available.
At-will Tactical Teleportation
Get a wand of dimension door – while it will require replacement eventually, it is much cheaper than an at-will cape of the mountebank, and has the further advantage of being a spell that you cast (albeit through the wand) – which makes it compatible with Spell Combat. The cape of the mountebank doesn’t have that feature. Since you can actually just cast dimension door yourself, you also qualify for the Dimensional Agility feat; for once, that feat is probably worthwhile, so you can continue acting after using it.
Using the wand will basically require that you only use one hand to attack, but that’s OK for thrown weapons.
Also, you could take Craft Wand and make your wands of dimension door; you actually have that spell. It will take three weeks to produce one, and cost 10,500 gp each. Note that summoners get dimension door as a 3rd-level spell: their slower spellcasting progression means that it still requires caster level 7th, but a 3rd-level spell at caster level 7th is still ¾ the value of a 4th-level spell at caster level 7th: a summoner could produce the wand in 16 days for 7,875 gp (and you could buy it from an NPC summoner for 15,750 gp).
Blindsense isn’t really all that good, and most options for it are overpriced. The eyes of the dragon are, in fact, probably your best bet with that much wealth. Still overpriced, but you can afford it.
Eldritch archer gets 2 + Int skill points, but is Intelligence-based so that helps. Ultimately, the 3.5 warlock also got 2 + Int skill points and wasn’t Intelligence-based, so this ends up being mostly the same, but sadly not better.
Alternative: seriously, try to port the warlock
This answer fails on a lot of levels to actually deliver on something warlock-like. I am actually surprised at just how frustrating it was to try to find better answers for you.
Paizo has an unreasonable position on at-will abilities, and is not likely to publish anything any time soon that will work well for the warlock. As mentioned, the kineticist is terrible. But Pathfinder changes little from 3.5, and the warlock would require very little modification to work in Pathfinder. Many, many people have done it; it’s not a problem. I strongly suggest that you do so, rather than trying to bastardize the character with something jury-rigged together from Paizo material.