1) Yes you can keep the chimes.
2) wont have anything to do with chimes so Yes.
3) you can keep your onstar w/ a certain wire harness.
4) Nope.
now with your questions answered. I have an 06 GP, I was pissed when I found out that my wiring harness costed $120 bucks to keep chimes and onstar, but all I could find was that harness. Pissed me off cause I dont care for that stuff. if u have 03 model and below, sorry I can't give a good refernce to that harness but they're expensive. This was the only type of harness they made at the time for my year GP...