GoldenEagle, I have 2 minor remarks about your PC:
1) Spell Focus: Enchantment isn't a metamagic or item creation feat, so you couldn't take it at 5th. You could have taken Empower spell, and them Spell focus at 9th.
The robe doesn't make you meet the requirements for Greater Spell Penetration. Besides, it's really useful only if you cast a lot of spells that affect others, and divinations don't. think if you really need it.
2)Vestment of the librarian should cost (10+10)^2+20=8,000 gp
so you should have spent 4000 gp and 320 xp
Reverse engineering the rope of the Archmagi following the formulas in T&B we have:
Spell resistance 17 =50,000
armor bonus +5 =25,000*0.75
resistance bonus +1 =1,000*0.5
Spell Penetration =x*0.5
---------------------------------------------------
Total =75,000
So, the bonus feat should cost around 11,500 gp. This way, Taven's robe should cost 74,500 gp, not much of a reduction. It works better if you drop one point of SR (65,000) and/or Spell Penetration (which you can always take as your 15th level feat) (59,250/69,250)
I'm sorry if I make you spend more, this was meant to help you