Rich
For my next build I'd go 2mm ply and not as wide with less rocker, maybe a 12'6" flat water racer. The plans are certainly detailed enough, just mark the plan outline onto the boards and cut and assemble. Just youtube "Kaholo" for examples or look here:
www.standupzone.com/forum/index.php?topic=12860.0 To keep weight down, I will just seal the insides with a wood sealer or varnish. The epoxy and glass on the outside isn't even required, but it will keep it from dings and add strength. Under where you stand could do with glassing for strength.
Think the Naish 12'6" would be an ideal template for a board, but would have a recessed deck.
Please contact me if I can help.