The RCM kit is a awesome kit!

No the stock body will not fit, it would be much to small... The jato bodies work good (proline's and the stock one), nitro rustler bodies (from proline), and then the RC10GT (I think prolines) And I use a T4 body on mine

Whats your budget on a motor? It can cost anywhere from 70 to 200....

You use the stock spur, and in the RCM store there 5mm bore MOD1 pinions, and you have to get the hardened ones (other wise they will get chewed up with the steel spur) And the motor mount is adjustable