I have one, here's what I know:
1) No idea, probably not.
2) Some games (Rage comes to mind) always select 60hz, most do not and 120hz works fine.
3) No idea. I think it was originally made for nVidia's 3d vision.
4) Yes, so you won't get tearing. There aren't many games that will go over 120hz anyway.
5) It doesn't hurt. I run 2 580GTX's in sli. But you'll still see a big benefit even without it.