It does appear to be a downriver kayak, and Bill has a good point. But... if you have the glass and epoxy out, I bet it wouldn't take but a small bit of a skeg bump glued somewhere behind the cockpit to render it very fun for flatwater use. It looks like a good hull shape.

I'd question if the kayak has bulkheads, likely not, and if not, why do hatches? Unless you're going to install bulkheads. Then there are deck plates that will make a decent hatch, and are a snap to install. You might need to reinforce the deck with some glass where you're going to make a big hole. I suppose you could do Valley style hatches as well, but I think the deck plates lower profile would work better offset one side or another from the deck ridge. I doubt you want to get into building recesses for the deeper rims on valley style hatches.

Combo storage float bags might be an easier solution... you're gonna want float bags anyhow... and even with hatches, unless you do a great bulkhead and install job, you're gonna want your stuff that needs to stay dry in a dry bag anyhow.

Deck rigging can be done a variety of ways. I'd be tempted to try Maroske style retro-fittings at least on the immediate fore and after deck I could reach from the cockpit. Greenly soft padeyes would be another good choice I think. Then there are screw or bolt on fittings.

I'd also consider under-deck rigging for pump, water bottles, etc.