Mosfet are easy. It's youre basic 2 wires from battery plus a 3rd wire that goes on your trigger. I use hamsterfet, easy to set up and fairly cheap.
Mosfet are only really needed if your planing on using lipo batteries. I put one on mine while I was upgrading for ROF and thought I might make the switch in batteries, I still haven't.
Well done mate, looks like you sorted you gun out by yourself. You've just saved yourself some coin and also gained something money can't buy; experience.