Just seen this, I've done a few bodies now and all I do is hand sand the original finish until it's roughed up enough for paint to adhere. I never try to take the colour off 'cos it's too much work.
Obviously use finer and finer paper until it's really smooth, then tack it and spray with primer sealer. About 4 coats works for me. Then sand it with wet and dry 1000 grit and leave it for a day. I then put about 6 coats or the contents of a 400ml can on and let it dry, I use car paint that my local MF will mix up any car colour for me. I'm going to do a Renault liquid yellow next
I let it dry for a couple of days and then use G3 to get overspray off and polish until unconcious.
Works for me, I've had some good finishes too.
HTH