If you want it to shoot over 400 then It will have to be semi only. This can be done by making a small modification to the tapet plate.(I don't personally know how) I would say do what you want to the gun.(TBB, Hop up, scope, externals) and see how you like it as it stands there. If you want to put the extra money into it then I would say upgrade motor, gears, possible the piston and I'd say put a mosfet in it. After all that, do the spring to make it shoot around 500fps.