Other considerations:
1) set the hatch so that the lateral edges are are close to or meet the curvature of the deck (or one edge on a day hatch). This avoids the recess forming a bowl around the entire hatch rim and so allows drainage, preventing water from collecting around the hatch while paddling
2) I like to add a layer of lightweight glass over the carbon fiber to protect the edge with the deck, although the epoxy fill is probably sufficient
3) I've used kevlar/carbon fiber instead of carbon fiber sometimes, and one could just use glass and colored resin for the recess.