There are plenty of tunes available that are proven from venders who have demonstrated both their technical acume and their customer service.
If you check out the threads related to the GMPP tune, you will find out a lot of real world experience and engineering data that was shared. The Kappa is a fly by wire car and there are a lot of well understood ways to add HP that allow you to go to just about any HP level you want in increments.
Basically, the best / most cost effective thing you can do for a 2.0 is install the GMPP tune which will give you a huge increase and maintain your warranty.
Both the NA and 2.0 will show significant gains from swapping to a high flow cat.
The exhaust and intake are not limiting until you get to high output numbers.
For the 2.0, the CAI does nothing but add noise. Same for the catback.
Charge tubes with a tune does improve flow and thus reduce the high RPM losses due to the factory charge tubes being limiting.
for the NA there are tunes, headers, . .. and best of all supercharget kits that will bolt on a ton of HP.
See werks, ddm, hahn, wade's garage etc for more info