RE: Substitution of wood materials
Whoa, stay away from the 1/16" ply sheet. Flexible, heavy, warp prone.
Thicker, lighter wood as others suggest and nicely sanded is a good way to go. Lighter then hard 1/8" should be absolutely fine, but ideally try to find some C-grain for the added torsional strength. No shame in using decently airfoiled light 3/16" either.
I think a lot of older 1/2A designs (perhaps some newer ones too) were on the porky side. I get a laugh out of reviews of 1/2A kits or construction articles that come out at 20-24 oz. My first scratch built 1/2A R/C aerobatic bird came out at about 11oz, with a flat 15% symettrical wing, I can fly it to my hand and catch it, and I've also thermalled it.
MJD