It will work but you are likely to get some cogging. I used the same motor with my MM and had bad cogging from a standstill. Once the truck gets moving, it is ok though.
It depends; the MM controller are pretty sensitive. rumour has it that that Y winds run better on the MM controllers. While some people don't notice any cogging on their neu/mm setup others are experiencing a nasty cogging. According to the engineers at castle the Neu motors are slotted motors and need a software update on the MM, which isn't available yet, since they are focussing on the MMM and the Neu type of motors. I am sure that once the MMM/Neu clone is launched the MM will get a 'slotted' option in the software too
The higher the number of turns, the cooler the motor will run in principle- input voltage will need to increase however to maintain the same speed (gearing up can only work to an extent before the motor & esc become overworked).
I imagine so- if all the hyper vehicles share a common center diff design, then the RCM motor mount should just bolt right in place- I would suggest looking around the forum to see if anyone else has done a conversion on the hyper8 and used that mount.