Welcome to the community.
Im going to start with the same thing i tell everyone. Drive the car for 2,000 miles before you change a thing. Drive it fast and drive it slow, drive early in the morning and late at night. Get to know the car, listen to it and learn what it likes. Then decide what you want to change. The first thing i would do is take it to a local tuner and make sure everything is running normally then i would just drive it. With Turbo platforms in general its a good idea to make friends with a tuner. If the car isn't tuned already you can unlock quite a bit of extra power with a proper tune and if it is tuned then a good tuner will be able to map out the future for you. It sounds like its setup for a stage 2 already so i would make sure your ECU is happy and the parts are all working in harmony.
From what your describing it sounds like the previous owner started with power, Im the exact opposite. If everything is stock I would start with some nice sway-bars and end-links, maybe some performance struts (10 years 100,000 miles) they probably need it anyway. If the brakes are stock I would look into stainless brake lines and maybe performance pads/rotors.
With great power comes great responsibility. Its more important to be able to stop fast than it is to go fast.
13 WRX Hatch - Torqued Performance Stage 1+
Slow is Smooth > Smooth is Fast