Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

the abjuration idea is OP.

a combination of your two ideas may be on a better track

focus abj: +1 level immunity LGI, GI
gr focus: +2 to number of spells that can be removed in a mords
epic: +1 level immunity LGI,GI

Enchantment

Enchantment focus = increase area of effect +1
Greater Enchantment =increase area of effect +2
Epic Enchantment=increase area of effect +3

most of the spells for the school are area of effect.

SF Abjuration: Your shield spell now also grants immunity to Isaac's Lesser and Greater Missile Storm.

GSF Abjuration: Your Globe of Invulnerability and Lesser Globe of Invulnerability now also stop Orbs created by spells.

ESF Abjuration: no idea, probably something with the counterspell mechanics.

Counterspelling is a good idea for abjuration. Don't forget, these feats aren't for the arcanist spell-book only, they are for all spell-books.

SF Abjur I: You gain +1 on your counterspell attempts.
SF Abjur II: You gain +2 on your counterspell attempts and you can now use any spell from the same school to counterspell a particular spell (not just a higher level one from the same school).
SF Abjur III: You gain +3 on your counterspell attempts and you can now use any spell to counterspell another spell as long as the spell you use is equal or above the counterspelled spell's level.

I like the counterspell idea for abjuration, and i also like the idea of increased duration for illiusions....or perhaps for the Illusion it focus it makes the programmed image spells partly real with lesser damage^^

If I recall correctly, the code used for counterspelling is a complete mess, so I do not know if it is feasible to plan counterspelling benefits in the Spell Focus Abjuration feats. That being said, I am all for buffs for taking spell focus abjuration, though I would have to relevel my character to get epic spell focus then.