i gotta 03 RS that we turbod. My shop makes the complete kit for this. comes with the up pipe, DP, intake, turbo, TMIC, FMU boost/retard controller, and voltage clamp. check out forcedairtech.com many people have our kit.
You can either do it with our kit or go DIY. all you really need for yours is the fuel and turbo and exhaust mani. I belive 05 RS can be opened sorced for tuning therefore you do not need the voltage clamp or boost/retard controller. As long your tuned right should be able to run 8lbs safely, this means a rich mixture during boost and plenty of retarding while in boost. This will in the long run shortin the life of your shortblock, but then throw in the sti 2.5 shortblock and run 17psi all day.
You can run the whole wrx setup. I.E: injectors, TMIC, turbo, exhaust mani, down pipe, you will need a wally 255 fuel pump, and a great tuner and i see no problem with you runnin 8-10psi. LMK