As far as the wiring, Im not too familiar with mosfets, but if you just put it in between some wires, there is plenty of wire going through the stock to install it... way too much, in fact. heh.
The gearbox connects to connectors that go through in to the stock and then on the inside of the stock, the connector connects to wires inside the stock. So its not all hidden.
Its a great gun though, I love mine!