Well, personally I'm running into analysis paralysis with feat, spell, and item choices. Since I can swap spells each day, and I don't start with much item-wise, I'm not too worried about those yet. I do for sure need feats, spell specialization, and starting spellbook, however, and any advice would be appreciated.
Also, Shadow, I need to ask about how many spells I can start with. Normally, I'd start with 7 1st-level spells and get 4 more spells from leveling, but I'd like to at least get some 3rd-level spells to start with as well (I don't get free spells for leveling mystic theurge normally, but I can still learn spells and copy them into my spellbook).