I would go with TEIN springs one of the best out there. And go with A PERRIN sway bay front and back. As far as exhaust thats something you need to look into. HKS makes A great one for the STI. But it all what you want as far as sound and HP. There are some companies out there that are making A front mount intercooler that is A drop in no cutting or anything like that. Anyway I hope I helped A little bit.
And Welcome to the forum
Good luck with the ride get some pics and post them