Good luck with your build and looking forward to seeing pictures. I built the Kaholo 14', very stable and quite fast, but its hard not to make it too heavy ( mine is 20kg). Epoxy is heavy! If I built another based on Kaholo, it would be about 25" not the 28-29" of kit, a pulled in tail at half the width and probably deeper sides , but with a recessed standing deck.
Lots of build info here.
www.standupzone.com/forum/index.php?board=11.014' is a good length for most races and down winding, longer is a hassle to store and put onto cars but longer is generally faster also. Flat tail is more stable, pintail generally faster. Try as many as you can and steal ideas for your build.