What's your budget?
I stayed at the Hotel Diana, which was pretty awesome.
ALso look at the Villafranca, or the Andreotti. All of these are close to the termini station which is the main transport hub, and you can easily walk the loop of Vatican, Colloseum, Trevi from there.
Regarding an ND I'm afraid I have no idea - just know I need to get one!
Also - you must go to Florence, you can get the train there very easily from Rome, its 40 euros on the fast one - 2 hours or 20 euros on the slow one - 4 hours. You can even book a flight home from Pisa if you don't want to train it back to Rome - bear that in mind.