and just to confuse everyone after they got the shape and size in their mind, I find nothing beats the flex and float of a PU surfboard. Some of the new technologies have recreated the flex of the PU so are the other option.
Ive got a few epoxies and they tend to be a bit corky for paddle surf and different flex. Ive found you have to put a lot more weight on the front foot to get the thing down the face of a wave. So if you going epoxy, then go down a size or two. epoxy is definitely an option for bigger riders,
Ive noticed a lot of the kite surfboards need a slightly flatter rocker than a traditional shortboard for upwind ability. Im not sure if this is just in the central part of the board or nose and middle.
otherwise I reckon concaves are one of the best inventions in the last 10 years.
So many factors

Once you found what works keep it and duplicate.