I usually use a couple of coats of a marine grade spar urethane to protect the wood and a topcoat of flat white for reflectivity. You have to make certain that the paint is compatible with the urethane, however.
Definitely primer, otherwise the paint doesn't preform very well at all. I would suggest a clear coat just to protect your hard work at painting. Also adds a few years of lfe to the finish
With enamal I usually just use throw away brushes. Easy clean up. I haven't used latex so not sure of its proformance. It seems to peel off walls though if the are moist so I'm not sure if I would try