Do a smaller project first .. please :-)
Go through the projects on this site, check out all the builds presented on "yoootoob"
Something that gave me some much needed experience was making a "large suitcase" i.e. a purpose built gun-case for a very large rifle.
I made a "plug" giving me the external shape for the box/case, and made a mould from that. That was made form MDF, but was much too heavy and more than strong enough for making the mould.
For a kayak, I would definitely try to borrow an existing kayak, maybe offering to repair it, before using it to make the mould from it. Alternatively, make the "plug" from low density foam, cut and sanded, and coated in Pattern Coat.
Depending on the use of the kayak, I would go for a sandwich construction using Kevlar/Carbon mix 200 g/sq metre as the outer layer(s) a foam core and the required number if inside layers.
This would be very strong and impact resistant. If yours building a pure straight-line racing kayak, go for pure CF and only a few layers of 200 g/sq m. then reinforce "strategic areas" with CF/kevlar flat braid.
Go to a club or the like where they have kayaks of the kind you would like to build, to see how they are made.
Good luck ...
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