Alright I've already posted out of the newcomers section on similar stuff but I need help..

OK, I have a 2002 wrx sedan, with...

Engine: IHI VF22 upgraded turbo,
Cobb engine management with AccessPORT tuned on dyno at 290 whp, 340 at the crank
Perrin uppipe & downpipe,
HKS Hi-Power exhaust,
Blitz SUS intake,
Greddy BOV,
Turbo XS Top mount intercooler,
PE 565cc Injectors,
Walbro 255 lpf fuel pump,
ACT street clutch

Ok, I want to remove the BOv and replace with stock one. I need a quieter exhaust and am looking at a borla hush. I'm not sure of everything I will need to do this...
If I order the borla catback, Borla Twin Tip "HUSH" system, such as from the link, and remove my current exhaust system, an HKS turboback, is that all I'll need, if I have gaskets? There are no cats on the passes emissions testing because of the tuning. Don't I need a cat to hook up my borla? And the BOV, can I replace with a stock one? Does the intercooler affect this?

I am very confused... I am trying to ask the right questions and read up on as much as I can, but I'm still very confused. I am 16, with basically no expierence with cars. I am signed up for an automotive class at school. I love the WRX, it's the first car I looked for when I was in the process of buying a car, and I wouldn't settle for any less of it. This whole situation is very distressing to me. I just want my car to be quieter and have better miles to the gallon.

p.s. I know how people feel about buying already modded cars and stuff, but the guy I bought it from did it right. I had a complete check and tune up a week after I bought it, and nothing was wrong. It runs great and everything works. The only reason I bought it was because it was the only affordable one in my area.