I stand corrected, true planking is as shown above. There is also "sheeting" whereby one covers the frame with 1/32" thick pieces of balsa sheet, but for display purposes use whatever you feel most comfortable with.
Turns out the post I was thinking of was actually made by Moostang:
http://www.virtualaerodrome.com/image_d ... &offset=36
To estimate the wood you need just rough calculate the area to be planked then add some extra. So for the B-17 measure the fuselage diameter at the nose and multiply that by the length. Yes, the fuselage tapers as you go aft, but that will give a little extra. Then go buy about 1.5x of what you calculated since there will be waste and errors made.
Don't worry about the wood used, a few mistakes will still only cost a $2-3 for a new sheet and you're bound to make some so buy extra. If you wind up with a few extra sheets you didn't need then explain to your wife that you need to build another kit to use up the extra.