Welcome to the boards. I hope you stick around. Ok. What I know is only a little about a little.
1) If you have a GTS, their's an XS Turbo kit (~260 hp) and EIP Turbo kits (up to 320 at 14 psi), in different stages. Blitz makes a Superchager for the GTS. The power is evenly distributed, but the max hp is only around 200 whp.
Dave Drafter(? newcelica.org?) has a custom GT turbo out. I saw one on eBay as well.
If you have money, you can have ANYTHING customly done.
2) Only if you get it customly done. I've never heard of neither the GT nor the GTS getting a twin turbo job. Not much room under the Hood
and the motors can't take much boost w/o major internal work being done.
3) Basic installs, such as cold air Intakes
, exhausts, headers, and piping can be done at most muffler shops. After that, you gotta' see what's available in your area.
4) Racing is all about hands on experience. That's about all I can tell you. Race a V6 at every chance you get, but be weary of V8's. That's the best I can tell you. hang around the boards and listen to some stories for a few days. You'll get the idea.
I hope that helped.