1. You won't need spring compressors to do the rear springs unless you are putting spacers in there as well, then it's a "maybe".
2. The plastic piece will actually come off your old springs & you can re-use them if desired. I think they're to prevent squeaking.
3. I don't remember for sure, but I don't think so.
Doing the rear springs and shocks is really easy, don't sweat it. Doing the front is a bit of a PITA.