I spent seven days painting the hull:
Day 1: Mask the varnished transoms, paint on the primer. Wait 24 hours.
Day 2: Sand the primer
Day 3: First coat of polyurethane. Wait 24 hours.
Day 4: Wet sand the first coat.
Day 5: Second coat of polyurethane. Wait 24 hours.
Day 6: Wet sand the second coat.
Day 7: Third coat of polyurethane.
With each subsequent coat of primer/pain, as I sanded them, I realized how hard it is to try to fix existing flaws in the finish by putting new layers on top of them. First, it's really hard to sand the last layer smooth enough and evenly enough to hide the flaws. Secondly, each new layer adds new flaws. As I mentioned, I think the right answer is to start with as smooth a surface as possible. It would have meant adding additional layers of epoxy before varnishing or painting. As I discovered with surfaces of the seats, sanding the 2nd layer of epoxy almost back down to the wood and then adding a 3rd layer (which is then sanded smooth) leads to a very smooth and consistent surface. Oh well, next boat.
I've now officially given up on having a mirror-smooth finish and have now settled for one that isn't too embarrassing to have other people look at.