I agree with the idea of using drills for drive, and the drill mod kits (avaliable from featherweights.org) make them very easy to use. As for batteries i think 3Ah is a bit OTT for most fights, 2-2.4Ah race packs should be adequate for most designs. Plywood is an easy material to machine and remember you can always replace it with polycarb at a later date.