When I first started building boats I used a lot of Thompson's water seal. It is good stuff. Yes...after it dries you can paint over it with an oil based paint. Thompson's is an oil based product containing aliphatic hydrocarbons. You have to wait around two months before applying a latex paint. In either case you have to use the appropriate primer. I just can't recommend putting epoxy on over it, though, with out testing it thoroughly. Most plywoods you buy today are made with waterproof glue. It is the wood laminations that are the difference. As a result almost any good quality plywood will work when encapsulated in epoxy alone....then coated for uv protection. Maybe someone will know for sure.