Externally I'd add as little as possible to get the job done, as guns soon get heavy and cumbersome. But it's your choice. I mean you could hang the kitchen sink off of the thing if that's what floats your boat.
Internally, a good clean and proper lubrication, AOE adjustment and decent shimming /motor height adjustment. Good lipos and Deans connectors. Feed it decent quality 0.25-0.28g BBs and get out and become a better player.
There's no point arbitrarily throwing 'upgrades' at a gun until either something goes wrong, or you've identified an area that actually warrants improvement.
