Everyone is giving great info! I've not tried a boat yet but I use kevlar to reinforce my new hockey sticks the rim of my paddle blades. Extends the life of both for a fraction of the cost. I've used fiberglass for small sculpture works along with plaster and resin molding.
As stated before, if you want to copy your existing boat, you can make the fiberglass mold right on it with release agents and filler. You don't have to make the whole mold and cut it, you can make the bottom/top halves in two waves right along the existing part line. The cockpit rim will be a challenge though with some creativity you can get it. I'd think a third, smaller sacrificial mold might be in order. Make each part with a clamping rim which is necessary for the actual layup process and useful for mold making at the same time.
RE: plaster. If anyone want's to use plaster as a mold be advised it's quite difficult to seal for vacuum processing. Plaster is inherently porous and even with moderate application of urethane sealers it'll leak and pull bubbles into your resin. Using it as a plug will work if you don't vacuum process the mold you take. A plaster plug, however, is ridiculously heavy, as is a plaster mold of that size. Foam is much easier to work with.
RE: materials. In my opinion, the best strength comes from applying an outer layer of woven kevlar, then layers of unidirectional carbon, followed by your glass interior scrim. That's also the most time consuming. Using woven carbon is still strong only you don't get the selective layup strength by applying unidirectional just where you want it. You can use woven carbon and selective touches of unidirectional (like on the tip and tail) for a mix and match approach. The possibilities are rather open. And don't forget to integrate your hardware so you don't have to drill any holes!
On the river, I can abandon who I am and what I've done. However brief it lasts, while on the river I am nothing important and everything insignificant. I am flotsam, and happy to be so.