Be sure to use Lite ply and not birch for everything but the firewall. That makes a very big difference. Balsa doesn't really weigh squat unless they specify oversized stock. I've seen a .40 size plane that was planked with 3/8 and sanded to shape. It flew ok, but was heavier than my b..ls. If he had just dropped down to 1/4 it would have been a decent plane.