To answer some of the questions -
Yeah, the glass helps the flex quite a bit. The 1/4 plywood is more like 3/16 so 2 layers is really closer to 3/8 thick rather than 1/2. A single layer is easy, keeps the weight down, gives it decent flex and keeps it all waterproof.
A hotcoat is a filler coat of resin only after you do the first laminate layer where you wet out the glass on the board. If you use too much resin on the laminate step the fiberglass will float in the resin.
I'm not sure of the exact weight, it's not exactly light though.
I've got a 3/8" thick plywood lightwind board that I glassed also -http://www.kiteforum.com/viewtopic.php?f=107&t=2353837&p=568768
Solid 3/8" all the way out and it also has a single layer of 4 oz. glass on each side and is super stiff. The stiffness is more a function of board thickness and this one is a bit thinner overall and the tips/rails are way thinner and the flex feels good.
Yes, polyester resin in not as stiff as epoxy. UV poly cures in 15 minutes in full sunlight so you can feasibly build a board in 2 days from start to finish. That's about it's only benefit. Vacuum bagging and epoxy would give a much better result.
Dimensions are 138 x 44
I didn't add a concave because it was a hassle. My plan was to make a few of these for my friends and I wanted it to be simple, quick, easy and cheap.
Lessons learned for the next one:
1. Find ABS for the rails or use poured epoxy.
2. Vacuum bag it, saves a ton of time, effort and sanding
We should have some wind in the next week so I'll post a more detailed ride review if I get a chance to ride it again soon.
Also, something that made it really easy was buying stainless snowboard inserts:
They were $5 for a 16-pack:http://boardcrafter.com/component/page,shop.product_details/flypage,shop.flypage/product_id,75/category_id,7/manufacturer_id,0/option,com_virtuemart/Itemid,1/
I just drilled a hole to their depth with a forstner bit and filled it with epoxy/glassfiber mix and set the inserts in then glassed over them. They even come with plastic caps so you can sand them down and glass right over them then drill them out when you're done with a countersink drill bit. Super easy and looks professional. Way stronger than brass inserts too.