I would shoot the same frame rate as the clips to be composited.
422 will give you a cleaner key.
HD will give you the most options
you will be cropping and keying out the green screen so i would use the aspect ratio that conforms best with project but i allways try to bring projects up to current standards to prolong their usibility.
keep in mind you can shoot in 24 or 30 over 60i and go directly to hardrive through the 1394 port giving you options other then just the p2 card.
the requirement is that it be over a 60i streem to capture directly from the 1394 port
use the capture now feature in FCP and set the preset to non-controlable device the use the mouse to start and stop recording.
i hope all goes well!
keith