I don't play a paladin, but I'm pretty sure your defensive stats are fine for heroics - at least they would be if you were a warrior. The only issues you might run into this late in the game would be holding aggro over DPS that outgears you, or running with a healer who's used to excessively easy healing with a tank in full epics. But as long as you can find people who can work with your gear level, there's no question that you should be able to handle most heroics.
I must say that the fact that you went through the trouble of properly enchanting and gemming everything shows you have the dedication to do things right, which makes me rather confident that you'll do just fine.
As far as where to start, opinions tend to vary. In my mind the easier ones would be (in no particular order):
- Auchenai Crypts
- Mana Tombs
- Hellfire Ramparts
- Blood Furnace
- Slave Pens
Ideally you should focus on instances you have tanked a few times in normal mode since you'll already be familiar with the pulls and boss strategies.
Hope this helps.