As far as experience goes we’ve done performance work on hundreds of these, not to mention I owned a WRX so we know what works and what doesn’t. We’ve also catered to all sorts of customers with varying tastes and driving styles. Taking the guesswork out of chosing parts will save him time now and money and headaches in the long run.
If your friend wants to give me a call or stop the shop by I’d be happy to go through some options depending on his needs.
-Mike