Get a new bucking (Systemas are good), nub (SCS nub is the best. H nubs are also pretty good), and a 6.03mm tightbore. (Madbull or Prometheus) You're better off replacing the hop up bucking and nub compared to just the barrel.
That's really all I would do to it for a while. A reshim/regrease would be a good idea. Adding deans would give you a slight boost in ROF and trigger response and is an inexpensive upgrade.
Don't start cracking open the gearbox if you don't have to.
As everyone else said, upgrade conservatively. Why do you feel you need a new piston, motor, etc right out of the box?
Put a bucking and spacer in if it isn't good enough for you AFTER a game with the thing. If you still need a touch more accuracy, grab a nice barrel.
After that, unless you HAVE TO HAVE more fps, more rps, etc etc... which you probably don't... don't worry about anything until it breaks.
Yeah, that's what I meant by it's a good idea. I'm not sure if E1 does any better of a job shimming/greasing compared to the original brand (Dboys), but I do know that most clones come with a horrible shim and grease job. If the OP is new to gearbox work then I don't suggest it.
Best upgrades are: BBs (I can't stress enough how much bb quality affects the accuracy), hop up bucking+nub, and a barrel. Start with the first two and if you aren't satisfied, get a new barrel.
Bioshot bbs are the best I've tried out of G&G, KSC, TSD, Goldenball, AE and BB King) You can get them at Bioshot.com. If you use G&G or Goldenball, then those are fine. KSCs are decent. TSDs should be avoided, they work and won't jam, but they give poor performance. BB King and Goldenball are about second in performance. Bioshots are definitely the best in my experience.
