Welcome to the addiction!
1) It's done when your specific gravity reading doesn't change for a few days. If you don't have a hydrometer and test jar, I'd suggest you get one. They're cheap and invaluable!
2) I know of a few people on here that bottle in plastic two-liter pop bottles. It's doable. I can't specifically comment on how, but I assume the process wouldn't be any different than using glass bottles with crowns.