If you get a heatsink, you will definitely want to get the motor clamp heatsink from Mike. As far as I know, he's the only one that sells one. It will hold the motor together. If you get a non clamp sink, the endbells will fall off at some point.

Where you attach the fan depends on whether you get a 5v or 12v fan. When running 4S, I just run a 12v fan straight off of the battery pack.

Why would you want to use mechanical brakes. The MM has excellent brakes.