ok, let me put my 2 cents in. i have never owned a subaru,although when i get back from basic i plan to by a wrx. but, the stock top mount is great as long as you dont:
A) turn up the boost
B) drive hard for an extended period of time
because the stock turbo suffers from that little thing called HEAT SOAK!!! i recomend going with the Easy Street Motorsports top mount intercooler for now. with the stock turbo, a new TBE, K&N Sti intake, and the ESX top mount, TSX RFL BOV ( turbo xs blow off valve ) you will have an awesome car. ( of course, add more mods as u wish...lol ) you should also get short shifter, ditch the stock seats-the side bolsters suck for serious driving and they arent good for harnesses( if you have plans for those), and look at a good suspension setup. i also like the look of the charge speed body kit,that is if u are into looks as well as performance. there are so many mods to make to this car, and mostly it depends on how u plan to drive it, your budget, and your taste. good luck with your car!