WDS won't work with WPA since WPA encrypts MAC addresses.
WIth WPA, I wouldnt' be as worried about the key length as the key rotation time.
With WPA2 you're much better off, but either way you're losing WDS capability.
Best bet is to connect multiple wi-fi routers scattered throughout the house via powerline networking back to a central router and locking them down with WPA2.
That way you have the best of all worlds with no cables to run.