if it were me, i would attempt to find a COD or wrecked late model STi and purchase that as a donor. this way, you would have subframes, wiring, transmission, axles, spindles, etc. EVERYTHING would be there for for a complete swap including 6 speed and necessary ancillary parts.

after that, its all labor. focus on getting the car operational first, then add supporting mods later to achieve the hp goal you have in mind.