[Bellerophon]

I'd say game it once or twice before messing with it. Any shortcomings will become apparent and you'll have a better idea what you want before you start buying stuff.
Once you know what you want, keep in mind that upgrading some parts (the battery, motor and spring are the usual culprits) will require you to do a lot of secondary upgrades to prevent a failure/get any noticable benefit, and the costs of these start to pile up quickly. For a lipo, you must research handling/care instructions and get a good charger/balancer to keep it from exploding, a MOSFET to keep it from burning out your trigger contacts, and rewiring to deans to keep your connectors from melting. Same story with the motor/spring, upgrading these without doing your homework will at best provide little benefit and at worse will tear your gun to pieces.
To summarize, try out your gun on the field, do your research (there's lots of information out there written by techs much more experienced than I am), make a plan and stick to it.