Go with with the Borla axle back muffler....it sounds a lot more aggressive when you accelerate and is "quiet" when you cruise.
Spacers is the cheap way to add a wider stance, but you'll still be on 17's.

Get a set of aftermarket 18's or 18" oem take offs. Anything beyond 18's would be senseless on the 2.5.
A quality air suspension setup is dope....but will be much more expensive upfront and in the long term due to maintenance of the air suspension. Consider a set of coilovers instead if you aren't comfortable with the cost associated with air suspension.
You should also consider aftermarket intake, front strut bar, and rear sway bar as well.