Basically get 16AWG wires and put them where the old wires were. Also get deans plugs. You can find them cheap at hobby stores or Amazon/Ebay. I got mine at clandestineairsoft.com. Also, if you can switch out that crappy G&G motor for an SHS or AMP high torque.
Regarding that MOSFET, I've heard it's kinda hit-or-miss with Infected Armory. I personally have zero experience with them. Also with active breaking, you run the risk of damaging your motor and battery. Epic Skills on this forum sells MOSFETs for as cheap as $15 or $20 and they're pretty nice IMO