[It's Just Eric]

your list of mods seems like your going for all around the nicest. But keep in mind... things like the stereo and the big rims weigh / slow the car down alot.
the 6 speed is probly the first thing that would need to be done. If your going to build the engine, youll need a tranny that can hold the power, and thats the strongest that comes to mind.Tom's SVX and Subafreak have alot of info on that.
As far as speed..you might want to consider just HOW fast you intend on going. Also keep in mind there are many aspects to speed..Acceleration, top speed...and even braking speed and handeling are considered aspects of speed (Negative and lateral acceleration)
If you want to get more power out of the engine, and have the FASTEST svx, youll need to replace the internals. They can hold about 7 pounds of boost without much trouble, but anything more than that youll need to do a rebuild with stronger parts and lower compression.Also consider you will need to do, or have done, some work to the ECU to have the proper afr, among other things. If your going for a N/A build (Which judging by your wanting a supercharger you arent) your motor is going to even more work to get the power youll need. You may want to speak to Harvey (Oab_au), longassname, Phast_SVX, or svxfiles about forced induction stuff, engine builds, ect.
The suspension setup thats stock is pretty great..I have no complaints of it, but thena gain Im sure if you plan on going in excess of 150 youll want it stiffer. Also for cornering and braking to get more force to the tires to the road.
you may want to keep in mind the hefty weight of the car. The sti 6 speed weighs about the same as the automatic, so dont count on much savings there. For straight line acceleration, a weight reduction helps a little..but isnt that big of a deal, but for cornering....youll want to shave some weight.
On a scale of 1-10, you better be a good mechanic or an engineer. Youll need to do ALOT of custom work to get the power your looking for