What other people said.
As for what motors to use besides the CIMs.... Those new 18V RS-775 motors from Banebots are totally sweet, and will own the FPs and RS-550s in practical applications any day of the week.
I know, I know. Sacrilege! Blasphemy! But when you look at the
actual stats (not what FIRST posted) you too will be a believer.
~270W power, 13000 RPM, 112 oz-in Stall. This thing has all the power of the RS-550 or FP, at lower RPMs, in a bigger package. Lower RPMs = less reduction = less losses. Bigger package = more mass and surface area = more ability to cope with heat. These puppies will do everything your RS-550s or FPs will do, only they'll do it longer and harder with less overheating and horrible burning smells.
But, you know, that's all just theoretical. Perhaps you guys should just wait till I get my order for 5 or so and empirically test them for ya first.