Doing a mould for just two hulls sounds like quite some work for a beginner at boatbuilding?

There are 18 foot plywood designs out there where you surely can re-use all the parts. Doing a set of Tornado hulls might not be a bad idea either as long as you are putting the 18SX rig on it. You can even fit the 18SX foils instead of the centerboards.

Scarecrow touches a very important point. Resale value for this one of a kind boat will not be as good as for a boat belonging to an established class. One should always bear this in mind, even if a sale is not planned. One day..
If you already are willing to invest time in building a set of plywood hulls, why not go for F16 hulls and fit your parts to those hulls. Might have to work a bit on the rig to make it fit in the F16 rules, but at least it would be part of a class.