Boat Finishing and Hatch Addition

I recently purchased a 1986 Holder 20 (think precursor to Ultimate 21, w/ less sail area and beam) in good structural shape, except repainting hull and deck is in order. Boat will be mainly trailer sailed in fresh water. Finish is original white gelcoat w/ molded in diamond pattern non-skid areas on deck. No blistering on hull. The deck has a few hairline cracks in the gelcoat near some hardware points, but core & laminate is sound. Interior is flat white gelcoat stucco.

The hull below the waterline is sanded to 120 grit from the previous owner removing old bottom paint, as are the rudder and drop ballast daggerboard. Deck and cabin top have had a number of hardware relocations and spot filling, so I'm looking at sanding down the minimal molded in non-skid and repainting the deck w/ new non-skid compound.

First question: What do folks recommend for the paint system below waterline, above waterline, on decks, and on interior? Should I go with an epoxy barrier shield before painting?

Second question: I'd like to add a 19 x 19 Bomar or Nibo foredeck hatch on the sloping cabin roof. I'm concerned this will interrupt a deck compression load path from the forestay to the mast base. My thought was to laminate 2 foam "beams" either side of the companion way at the bulkhead and run them either side of mast and foredeck and then have htem meet at the bow, below the stemhead fitting. Cap them with uni carbon and some biax. Think this is in order, or am I worrying too much?