Let's see... all WotC sources permitted?
Feats:
Faerie Mysteries Initiate negates the need for much Con when you use the HP form (still need it for Fort saves, though). Combine with
Vigor to overcome your d4 HD by a lot. You also need both Quicken Spell and Quicken Power (because you've got more casting than actions). Get
Schism too, even if you need to burn a feat to do it. It's that good.
Alacritous Cogitation cuts way back on the guessing game of what spells you'll prepare today. Keep a good general list, leaving one spell slot of your highest level open, and once per day, you have the right spell for the job (provided it's in your spellbook at all).
Other feats depend on what you want to do. If you want to be a crafter, take item crafting feats. If you want to de-trap, take Elemental Summoning and either Fiery Burst or Invisible Needle (reserve feats, Complete Mage; Elemental Summoning gives you something you can renew every round to spring traps, while Fiery Burst of Invisible Needle gives you something to use to zap the trap until it dies; you'll want to combine with Detect Magic and Permanency, or a way to boost your caster level, Arcane Sight, and Permanency). If you're after a particular PrC, take it's pre-requisites.
Powers:
You want Psychic Reformation (it's a must-have), Vigor, and Schism (as mentioned). Your Psion side gets a lot of really nifty low-level defensive powers - Force Screen, Inertial Armor, and Defensive Precognition take the lead here. Also, you'll want to put powers that you'll use repeatedly on the Psion side - teleportation, direct damage, and the better Psionic Save or Lose abilities. You might also want to look at Incarnate, as it lets you take racial abilites.
Wizard Side: Specialize. You can get the better choices from your forbidden school on the Psion side. So Specialize.