Nice man! What's the deal on the used 2011 STi?
I'd hold off on the intake until you hear one in person, they can get old day after day. They Q300 is nice but it does drone a decent amount especially after a few thousand miles and people in the rear seats will complain.
And don't worry about the emissions, just get a catted downpipe. My personal suggestion would be to get the AP first, downpipe second, then a cat back and intake once you hear a few in person.