Floppy disks are OK, but floppy surfaces make bad bedfellows. Only knowing the prop size and not the engine, servos or plane, my best guess would be to aquire some aluminum servo arms as used on the 33% and larger models. Sure Link and many others sell quality giant scale accessories to fill your needs.
http://home.earthlink.net/~surelink1/index.htm
http://www.donshobbyshop.com/
The prop thing? Rpm and spool up time are considerations to different types of flyers. The CF props are great for flywheel affect etc. and the wood props are good for comin on right now. If all you can get is the wood, keep cutting until you are satisfied. The 20x8 should be tried as is first and take it from there. You may not cut it at all as the pitch just isn't there.
I've never tried the dowel technique. I have turned down aluminum to fit inside a larger prop shaft hole to use in a smaller one though. Your call on that one_bob