At levels 1-2, you're an psychic arsonist and poisoner. At levels 3-5, you're a poison wholesaler. At levels 5+ you've got fantastic spellcasting.
This is a separate answer because it takes a very different tone than "don't play one." The Erudite, (even spell-to-power) prima facie looks unplayable. A wilder starts off better and has a much more specific focus. A psion has a much more clearly defined "I'm a spellcaster. I buff myself and then X" role.
The best way to think about an erudite is as a fad-chasing "Top-heavy" spellcaster/manifester. They will (almost) never ever bother with buffs, almost always use their highest-level powers and spells to exclusion, and under no circumstances should they have damage-dealing spells (they have powers that work better for that purpose). I'm going to keep referring to spells because a spellcaster can pull off these tricks. A manifester, not so much. Only your "highest" manifester level matters to you (most of the time.)
I will recommend starting as an Elan Erudite. The bonus power points and the means of mitigating damage are incredibly handy starting out. If you have a party that will protect you, start out as a Kalashtar or Synad, according to taste.
Necessary skills: Concentration, Psicraft, Spellcraft, Craft(poisonmaking), Knowledge(Psionics) up to 5, Knowledge(arcana) up to 5. Skill tricks to taste.
You want craft(poisonmaking) because a) it's a fantastic income source for downtimes via the production of salvo, and b) you need it for psionic minor creation later. Figuring out a good sales route for your posion makes for either a fascinating backstory or a great first quest.
Levels 1 and 2 are going to be rough. At level 3, spell-to-power kicks in and you can start learning all sorts of awesome save-or-win spells (sleep, color spray) and "I'm in a city, buff me" spells (improvisation). At level 1, you're a "pure" caster, without access to any discipline spells. (And let's not get started on level 0 cantrips that still count against your unique powers limit.)
At level 1, you don't have access to any really good AoE save or dies. Your goto powers will therefore be:
- Control Flame
- (Make sure to spend some of your starting gold on a lantern and tindertwigs). A 1 damage no-save for the entire combat is... not actually that bad. When combined with the good chance to light enemies on fire for 1d6 continuing damage that consumes actions to put out, it goes to "really good." If you're only allowed one power in your adventuring day, this can last for 6 encounters (2 class power points, 2 bonus power points from high int. 1-3 power points from race) and be a meaningful battlefield control for all of them. Do try to appear as if you're hiding scared in the corner or something: you don't have to visibly direct the flame, and enemies are less likely to prioritize a scared little... hostage in the corner.
- Entangling Ectoplasm
- Better for short adventuring days, gluing enemies to the floor is a remarkable benefit to your party.
- Matter Agitation
- A competitor to control flame, control flame is better for long adventuring days, matter agitation is better for boss battles. Note its close range warily, but there are some days when you want to glare at someone and make their hair catch on fire. This is for those days.
- It's a bad day when you need to open with this. But bad days happen.
- Some times, you wake up surrounded by enemies. It's then you cast demoralize three times in quick succession. Remember, fear effects stack.
- Grease, Psionic
- If you anticipate lots of group battles in enclosed spaces, grease and a crossbow isn't a bad combination.
Grab the launch object cantrip. If you're in the mood to play artillery with AoE poisons, this allows you to do it.
What it comes down to, in your first level, is to get a feel for the upcoming day. Lots of enemies promised? Control flame. Big bosses? Entangling ectoplasm or matter agitation. An early morning ambush? Demoralize. A really really bad day? Vigor.
For your first feat, go for Azure Talent. Bonus PP are bonus, and if your DM is cool with you being able to spam low-level spells and powers (at level 3 with the Azure Talent + Pycarnum Infusion), all to the better. Make sure to speak to your DM about this, as there are many different interpretations. I would, personally, assert that a recharging pool of 2 bonus PP is easily worth 2 feats and the move actions necessary to power it, as it extends your adventuring time-per-day. If your DM doesn't like incarnum, go with earth sense, in preparation for earth power (and very specially designed platform boots). A really good case can be made for the Master of Poisons feat if your DM isn't a fan of Azure Talent. If flaws are allowed, absolutely take this, and some arguments can be made that it's more valuable (at low levels) than 2 extra PP.
Surviving is a matter of conserving your PP with long lasting powers (which is why Control Flame is on the front of your list) and managing to look pathetic to your enemies, so that they save you for last. Dress like a prosperous merchant and make sure some other party is carrying the lantern and tindertwigs for your fuel. As an elan, you can burn PP for HP, but if you're doing so, your party has done something wrong. At the end of the day, be creative in your situations, set up ambushes (with cheap traps from DMG2), and make sure your party is OK with running away early if the battle looks too tough. With 5 HP, no armor, and no capacity for self-buffing, your only defense is to appear harmless. Be like Tucker's kobolds and don't behave like a stupid meatshield. (Disguise, Bluff, and Diplomacy are fantastic cross-class skills for you, if you somehow have the points free to take them.)
At the end of the day though, your primary contribution will be via your crafted poisons for the party. It's a great downtime force-multiplier and can rapidly turn the tide of a tricky battle. Your default combat poison should be sleep-smoke, since it's so cheap. It's an inhalation poison, so try to let your rogue deliver it for you. Or, if necessary, use launch object to deliver strategic packets where you need to. While it's not the sleep spell, it is a nice save-or-win that's about the same.
In level 2, it's more of the same. You have two powers per day, and more PP. You can afford to preemptively vigor yourself, while maintaining the same power choices as level 1. Don't take direct damage one-shot powers here, either. That's why you have a crossbow. Save as much money as you possibly can.
In level 3, the world starts becoming your oyster. You gain access to level 1 spells. Avoid direct damage spells at all cost, but make sure you pick up sleep, colour spray, hideous laughter, cure light wounds, and improvisation. (And say goodbye to 250gp). Find a shaper and do whatever you have to do to get access to psionic minor creation. Make it a major quest if you have to. When you're done, you'll be able to make cubic feet of black lotus extract. Consider reading the poison-making handbook, then read it. Consider also the utility of a cubic foot of burning opium (try to have a fuse) launched at an enemy encampment. Between level 1 spells that you can spam all day long and psionic minor creation, your place in the party-value-hierarchy should be well-enough established to get some nice protective gear or buffs from party members. You'll want to finish the earth power tree, or the incarnum PP generator tree. If you're going the master of poison route, pick up earth sense here. You may want to pick up the feat "Supernatural Transformation" but this will likely continue to cause issues from your DM.
There aren't any notable powers worth earmarking your "utility" slot for, as it's much better served with minor creation.
Level 4. It's worth learning levitation, as that can completely negate melee-only enemies. Since you have 3 "slots" you can earmark the third for "personal defenses", as your first two will likely be "damage over time/save-or-win spells" and "minor creation." (Be as generous as you can be with your poisons. They're free after all.) Control fire isn't worth augmenting. An augmented inertial armor of +5 AC for 4 hours is compelling. The share pain combo isn't worth the opportunity cost. Inevitably, however, this third slot will be taken up by an emergency spell that simply needs to be cast. That's OK. You have fire and poison. Benign Transposition may save your life, or (so long as your party has a singular flying... friend), give you a way to get around all sorts of obstacles. Grab astral construct as well, simply because by this level, it'll last long enough to be relevant and you can encase people (yourself for armor, or enemies for... not armor) as you desire.
Level 5. You're four levels away from metaconcerting any utility powers you need, so you're not god yet, but you've at least survived the lava-filled foothills. For these feats, it's worth taking the excluded fork above. Grab as many seer powers as possible. They won't come in handy often, but some days you'll be all about the short-circuiting of detective plots. Your survivability is directly proportional to your ability to play being a tag-along follower with the group. Yes, when you "cast" spells, you have to use verbal and somatic components (boo), which gives you away, but much of your action is going to be an archery duel, or watching a flame flit around the battlefield.
If your DM decides to target you, you're dead. You've got emergency healing on tap by level 3, but at the consequence of not having powers available. Your saves are worthless, and you have no defenses to speak of. If you can take supernatural transformation, all of the somatic issues attached to the thing go away, which simply means figuring out what kind of armor to wear. By level 5, you can learn the spell heroics, and can grant yourself armor proficiency thereby, but it's not an effective situation unless you can start crafting custom items. If you can craft custom items, take the feat at level 3, and many of your woes disappear (as does most of your gold and XP). If you can't, then take advantage of the indirect approach of plentiful poison and arson and don't confront your enemies head on.