You use a 10" square of background fabric to get a finished square that is 4.5". You're correct that you need 256 of these. You can *probably* fit 4 squares across the 45" fabric. That means you need 256/4=66 strips. 66*10"=660"=18 1/3 yards. Of course you would want to get extra for shrinkage, squaring off, etc.
I have never made a CW quilt, but I don't understand why you need 22 windows for each 16 squares. Can anyone explain this?