Cant really tell ya what grit to use, all depends on the condition of the existing finish. If you cut too far, it turns the flake silver as you cut the color off the mylar. I'd prob start with 1000 and go slowly using plenty of water in a fairly inconspicuous location. Personally, I'd recommend a lot of couch surfing, look over the threads and other internet sources and videos before jumping into it. And just for safety, if ya plan to work on it in a shed with a wood burner, make sure you get the fuel out of it, the bilge can trap fuel and vapor for a long time. Go enjoy it for now, plenty of time over the winter to make pretty.