Honestly Peter, the cheapest answer is to do as I'm doing and just buy 2nd hand panels for it, they're so ridiculously cheap now. I couldn't paint it myself for less money by the time I've bought all the materials and the PPE.
I assume the clear coat comes off some resprays because the clear went on too long after the base coat.
The base coat I use on my classic, Deltron BC, says coat with clear between 15 minutes and 24 hours later. The clear I use says to put it over solvent base coat within 1 hour. I go with the 1 hour but because I suspect that I may put base cost on a bot thicker than a professional would I do wait at least 45 minutes.
The waterborne basecoat I have used on modern car, Lechler Hydrofan, repairs is a 30 to 40 minute interval before clear. I give that the full 40 as I am not painting in ideal conditions.