Problems with my fiberglass resin

In learning to use fiberglass resin to work on paddle and surf boards, as well as boats, I am using other projects to learn, projects where mistakes aren't as costly.
So here is what I've run into this weekend, and can't figure out.
1) What would cause the resin to crackle as it drys? This would be a subsequent layer, #2, or 3, while the initial coat was smooth.
3) Why do some graphics, vinyls, shrink up after the resin is applied?
4) Could applying the resin over coats of Byer paint be an issue? (Can I use Byer paint over the resin after it sets?)

Thank you all in advance for any advice and information. There is SO much information available when I search, it's hard to know what is good info...