I like that you recognize the fact that the current paint job is a good substrate to paint over. Too many feel it needs to go to bare metal which is not required in most cases.
You are not going to need any epoxy primer unless you end up with large areas of bare metal. Epoxy is only for bare metal as a rust corrosion inhibitor.
Perhaps you meant Urethane High Build Primer? UHBP is the last coat before painting and final sanding it in 180 would be too coarse of a grit. The Technical Data Sheet from the product you end up with will describe exactly the grit you should use.
After HBP is blocked out, then you can paint.
Going over acrylic enamel with UHBP is not going to be a problem like it would be if you were priming over lacquer... better to do a small test area first to see if it wrinkles your finish before you start hosing it on regardless... you just might have lacquer on it... A solvent wipe would do the same test.
Good luck with your paint job!
