I would get some steel bushings, an m120 spring, spring guide, maybe new piston depending upon which jg piston is in it (they have a supercore clone in some guns that is pretty decent).
Modify 6mm or 7mm bushings (depending on which gearbox you got)
Madbull m120 or Guarder SP110 spring
SHS Supercore clone piston
Modify V3 spring guide
alternatively Guarder, Modify, Hurricane, etc... all make upgrade kits for your gun making it a one stop shop, and they will usually also include a piston/cylinder head.
JG motor is actually pretty decent and could be very good depending on which motor you got lucky and got.
That will put you at 400 fps and fairly durable, if you decide to improve accuracy also look into a tightbore barrel, madbull, JBU, prometheus, systema, edgi, pdi, all depends on what you want to spend...
Welcome to the wonderful world of tricities airsoft, it was a pleasure shooting and getting shot by you today (I was the old geezer with the M14...
)