#1 well, as far as int goes, you're a disc priest and have said yourself you never run out of mana and your mana regen is decent. So, theres really no need to stack it, for a priest it just provides more mana pool and a slightly higher crit rate.
The talent bonuses you get from spirit are much more valuable.
#2When i cached your armory profile it said your enchanting was still at 30, I'd work on that (for the embroidery you can do to your cloak, and of course chanting your own gear is nice as well). My spell power unbuffed is around 2600, I don't know exactly, but ICC is prolly around 2500 to heal effectively. So, you're a little low there, but if you switched some of those half and half gems for full on sp it could help that number. Your haste is okay as well, I mean overall gear is decent just little things
3#Do you have a good rotation down? and are you quick to react? are pretty big things as well as far as disc healing, you don't have the enormous POP! heals others have, it's more about damage reduction so you have to be quick on your feet.
#4Oh yeah, change those mp5 chants for spirit or crit or something else. Hope this was helpful
Ive been playing my priest for a couple years now so drop me a line if you need any more help. Lok'Tar my Dwarven friend.