you can definitely 'chip' the car for a good ~40hp gain or so......APR, REVO, GIAC are some of the company options for that. It runs about $500+ for a chipping, and pretty well worth it!

I have a Borla exhaust, and it has alot of 'bass'.....but i love the rumble, and after a few months i've become used to the grumble and LOVE the presence it has, especially on cold new york mornings....but some people don't like the cabin drone it creates.

these cars ALWAYS get alot of attention! so get used to it and enjoy it! Sorry about your early expenses, but these cars do often require some maintenence, and most of the issues you've mentioned are the more common issues that would have happened sooner or later...so at least you're getting them outta the way! :)