1. In the Shadows of the Empire novel, there is a scene where he removes his armor/breathing apperatus and using some Sith healing technique to heal his lungs enough to let him breathe normal air for a few minutes. I suppose he can probably do the same thing to eat.
2a. I have wondered the same thing 2b. Yoda force moves it?? I don't know that one either.
3. That has been a question asked for years. I don't think anyone knows.