Wow, you've had a plethora of cars! Post some pictures of the previous rides if you have them!
Make sure you research and learn as much as you can about the STi platform BEFORE you begin modifying like crazy! These cars can be finicky when it comes to modifying them. Learning from other people's mistakes is free and is a crucial aspect that separates a happy ending from a disastrous one!
I'd suggest you start a journal and update it with your plans on what you'd like to modify and we'll chime in whether we agree or disagree based on our experiences. It's also a good way to look back on your journey. :tup:
That being said, I know you're going to love your new ride! I'd recommend you read the owner's manual once, or twice, if you haven't done so yet. You should also get accustomed with being behind the wheel, learning as much as you can about the car and how it behaves on the road when you're not researching online. "Driver mod" is going to be your biggest bang for the buck in terms of return on investment due to it mainly being free (for the most part. I know fuel isn't free.

).
I hope your experience in the Subie world will full of positives and a GTR would definitely be an amazing step forward after your chapter with the Subie ends!