Can you use AS for an action before revealing the dial while sitting on an astroid?

Yes, asteroids do not prevent you from taking actions. They just make ju skipp your preform action step when you land on (or your template overlapps) them.

Yes, you can definitely do that. I accidentally landed Xizor on an asteroid once such that any normal maneuver would have his template overlap the asteroid again next round, but one of his sides was clear of the rock. So, when his turn came up to move, I used advanced sensors to barrel roll him off the rock and then flew away clean.

It's worth noting that you can't barrel roll or boost away from the rock if the boost or barrel roll template would still touch the rock, though.