[Stealth]

There are 2 approaches to this. If you're going to want to only open it ONCE and only once, then by all means replace things that you anticipate breaking. On the flip side, personally I recommend replacing things as they break so you get your moneys worth. Why in the world, as a retailer, would I recommend that? Because I've been in the same shoes as you and throwing money at problems doesn't help you learn.

I have to disagree with Maciek on the AoE corrections:
If you're opening up the mechbox, check the AoE and correct as necessary. Hot spring or M90, it should always be corrected either via the sorbo+neo or nylon washers on the piston head. If your AoE is bad, it'll just shorten the lifespan of your piston.

You don't *need* the POM piston head until your stock one breaks. The G&P one is pretty decent.

G&P barrels I find have been pretty bad - inconsistent is the word. It's like they just buy whatever brass tube is for sale that week at the metal mart. Sometimes you get a winner, other times it's horrible. Upgrade the hop-up rubber. From experience, you'll see the most gains from that and it's half the cost of a barrel.

Lastly, grab one of our lipos for some good trigger response indoors. Look at motor upgrades when you're ready as the G&P M120 motor is quite slow to wind up.