Remember, you qualify for Incantatrix @5 so you can enter it @6. Also, the Otyugh Hole wondrous location (Complete Scoundrel 151) gives you permanent Iron Will. Saves you a feat.
I'd go at least something like this:
Human Generalist Wizard5/Incantatrix10/Archmage 5/Incantatrix+X
1: {Aggressive}, {Murky-Eyed}, {Noncombatant}
1: Eschew Material Components, Improved Initiative, [Scribe Scroll], Spell Focus: Whatever
3: [Iron Will], Spell Focus: Whatever
5: [Extend Spell]
6: [Persistent Spell], Skill Focus: Spellcraft
9: [Quicken Spell], Craft Wondrous Item
12: Craft Magic Arms & Armor, [Easy Metamagic: Quicken Spell]
15: Craft Construct, [@METAMAGIC FEAT@]
16: [Mastery of Shaping]
17: [Spell Power]
18: [Spell-like Ability: invoke magic - Just use shrink item on a focus to keep it hidden], -=FEAT=-
19: [#HIGH ARCANA#]
20: [#HIGH ARCANA#]
21: Ignore Material Components (if you want)
By my analysis, Irenicus is level 16 or 17. (He can be higher, but there's no great point.) He's a mage of awesome power and can do pretty much what he pleases throughout the planes. Adding levels to him doesn't increase his power that much, but go ahead if you so desire!
