MuttDriver:
What kind of capacitors should I use for motor noise suppression?
That's a tough one. I've never worked with such high-current motors, so this is outside my experience. But I suggest you look for capacitors with low ESR and large terminals, because they are going to have a large 20kHz or 31kHz ripple current going through them, and you don't want them to overheat. Maybe something like http://uk.farnell.com/vishay-bc-components/bfc238680474/capacitor-snubber-0-47µf-1250vdc/dp/1289281.
Locate the capacitor close to the motor. To reduce the surge current when the mosfets turn on and the capacitor charges, I would connect a small resistance in series with the capacitor, maybe 0.05 ohms, and/or a small inductor between the mosfet drains and the motor (but be sure to connect the flywheel diode to the mosfet side of the inductor).