Take what I am about to say as assumptions, because that is all that they are. The epoxy and poly will not have a chemical bond to each other, so it would seem that you would need to sand the epoxy to give the poly something to grab onto. Likewise, you would need of sand between coats of poly for the same reason. You should be able to do that sanding with a pretty high grit, like 300. As to what finish is best to rub out, I have no idea really, but I would think that you could do that to the epoxy without the need for a topcoat. You could probably look through the info on west systems website to see what people do to make those fancy CrisCraft type boats look so good. Good luck.
-- "Never measure......cut as many times as necessary." - PeteMoss
