Sucks it was used, you are pretty screwed I believe.
1. Yeah cheapest is ebay then get raped at dealer for setup/program.
2. Could ask the dealer, maybe they'll be nice and have an extra. Otherwise check junkyards or something (other vehicles may work),
http://car-part.com
3. Check ebay prices maybe.
4. They don't have much tread to begin with. Size should be on the tire.
5. Some goo gone or something like that. "Oops" paint remover, degreaser, etc.