1) I'm not sure what Steam's requirements are. You'd think a service labeled "Steam" would be okay with steamy stuff, but I dunno.
2) Pfff yes
3) It's still a bit early for this, but some kind of post-game mode I do have in mind, so the player can go back and collect things, achievements, etc
4) Hah... yeah, but only a few. I just spent several minutes deleting all my FF13 saves the other day and it was pretty annoying.