Welcome to the community,
I'm sorry you got the brunt end of the best/worst part of driving a Subaru. Everyone and their mother thinks they have something to prove and you will find a great deal more drivers who want to race a Subaru than most other cars. They feel like they need to test their metal on something that they know is a very fast machine. Cant tell you how many Hondas, Mazdas and Fords want a piece. Even with my mother taking it for a drive there were drivers looking for trouble at every red light.
That said we also have one of the strongest communities to lean on. We all have a special place in our hearts for other Subarus and their drivers.
As far as tuning goes I've said it a thousand time. Please learn how to drive your Subaru first. The STi is a wicked little animal by any measure and there is no training replacement for miles on the odometer. I usually recommend putting a few thousand miles on it stock just so you can get a feel for how it handles, how it likes to be pushed, and where the soft spots are. That way you can compile your own list of "important" upgrades. It all depends on your personality, I'm a canyon driver at heart and a set of sway bars, end links, and bushings made a world of difference for my driving style. I also definitely recommend an access-port, the stage 1 upgrade us usually enough to take care of the soft spots in the OEM tune and it gives you the ability to play around with ECU maps until the cows come home.
If there's anything we can do to help please don't hesitate to ask
Welcome to the community, Hope to see you on the road.
13 WRX Hatch - Cobb OTS Stage 1