: -snip- But make sure
: it's absolutely necessary, I'd check with Nick. -snip-

Ain't nothing thats absolutely necessary. But, some sort of rib of reinforcement material at the front and back of the cockpit is a "good idea. It is less useful around the hatches, but the bigger the hole, the more useful it is. "Carbon fiber will be stiffer than a similar weight worth of fiberglass. Kevlar is probably not worth it unless you have some kicking around.

You need to decide how hard you are going to be on your boat, how much you weight, where is the nearest bulkhead, etc.