That's a rather... powerful... class, to say the least.
Take Divine Vigor or Divine Shield for your Divine feat at level 6. CHA to AC is nice, as is 2xHD in Temp. HP and +10 Speed - both effects last the encounter, assuming a decent CHA.
Why not take Battle Blessing, though, for Auto Quicken on all your spells? And I'm assuming Leadership is a no-no. Try for Sword of the Arcane Order, too, if you can tweak the fluff.
Feats:
Human - Weapon Focus (Longsword)
1st - Power Attack
3rd - Practiced Spellcaster (Paladin)
6th - Sword of the Arcane Order
8th - Law Devotion
9th - Battle Blessing
12th - Awesome Smite
15th - Smite Fiery Foe
18th - Sun Devotion