Well, the performance of an STO isn't anything to sneeze at, but if you really do want to squeeze the most out of it possible, there isn't really all that much you need to do. First put in a good low pressure valve such as the Rat 3:16, MacDev RED, Maddmann Rocket, or Tornado, along with the proper springs. Next I would recommend switching the 3way to a Shocktech Bomb (I wouldn't be without mine, let's put it that way), and if you'd like, the front reg to an FGP or Jackhammer...or save some time and money by just simply getting a Belsales Twister kit that allows you to adjust your Sledgehammer externally. Vertical regulator is another high priority, second only to valve (and even that's debatable), but unfortunately likely to be the most expensive upgrade you can get other than the most expensive of barrels. I personally would recommend the Messiah or Black Ice or Gladiator. Bolts are, well, just another piece you can switch to lower the pressure, which is good but not critical. However, a benefit of delrin bolts like the Shocktech Alien and Superfly is less weight (speeding up cycling a little) and no lubrication necessary.
It's your gun and your money, so you can do however little or much you want with it. Personally I'd keep upgrades as simple as possible and spend according to what makes the biggest difference rather than what has the flashiest brand name. Upgrades can really make people look stupid when considering what they'll pay for 1-2% more performance for 200-500% more money. Don't feel like you have to be a millionaire or a moron (often both) to have something that shoots the way you want it to.
