I thought about increasing the Wiz levels (to get Blink) but I pretty much decided against it. Improved Invisibility cast by another party member is just as effective. There's really no other 3rd lvl mage spell that is very important when the party is lvl ~30, but 19 lvls vs 18 lvls of cleric gives an extra spell at lvls 5, 7, and 9. Maybe I might reconsider once I get to lvl 29.
This build doesn't really need much in the way of feats, since it gets extras from the fighter levels anyway. It takes all the decoy-type feats, adds specialization, finesse, and dual wielding for combat effectiveness (to partially counteract Expertise) and a cleric enhancer (GSF: Enchantment).
I will be choosing a specialist - I'm just not sure which one yet, because I forget all the opposition schools. I know I want to be able to cast Conjuration spells (Mage Armor and Grease), and Illusions, of course (Mirror Image); it would be nice to cast Enchantments (Charm Person) because it would gain potency with the GSF: Enchantment. I'm thinking Transmuter, although I wouldn't be able to cast Shield (Abjuration). However, there's a couple of Shield rings and an amulet.
Be warned that this character is definitely vulnerable early. It's not so much that the character is bad (although Expertise can only give +2 AC at Mk3) as the party hasn't attained many critical buff spells. I had to reload a few times until the character reached lvl 5 (squatted at Mk3 to attain Ftr2 and not take an XP penalty).