I believe our rims are already 7.5", but correct me if I am wrong.
I didn't say that I would actually do it, just that if I did everything possible in GS, that's what it would amount to. The cat-back wouldn't really do much of anything, and the cage wouldn't really make a difference unless I had a full spec suspension to tune and take advantage of the stiffness.
Don't waste another minute waiting on parts, or anything else. Just get out there and start racing! You will suck at first, and you will be slower than many other cars, but the only thing you will regret is not starting earlier...