tm mp5s are very weak. I can't imagine why anyone would pay that much for a gun that still needs parts and a shim job. You can get a jg metal body ras for less and have to change less parts.
If you like the mp5 for it's compactness, skip the fullstock. It just gets in the way.
Get a bigger front end to hold a larger battery.
Grand Poobah of T.W.A.T.