The 2012 Camaro SS has two engine choices:

1. All autos get the L99 400 HP motor

2. All manuals get the LS3 426 HP motor

Reliability is not the best as it is GM and issues do crop up. As for modification, it depends how far you want to go. I've built them from 500HP builds to 1500HP builds. Depends on your wallet. 

The engines are still old pushrod technology, so reliability is fairly good PROVIDED they have been properly maintained, which almost no Camaro owners do in my experience. Definitely have the one you want inspected by a mechanic prior to purchase. Guys/gals beat them hard and put them up wet, so finding a good one is tough. 

The motors as mentioned are pretty solid, but the transmissions aren't the best. Definitely have a mechanic check the OBD-II data with a scan tool to see how it is shifting if it is an automatic. If it is a manual, be sure the clutch isn't burned up.

I've owned a few of the 5th Gen Camaros, and while fun the reliability hasn't been great. My 2011 was in the shop with under 1k miles on it brand new for replacement of the drive belt which was non-adjustable and back ordered. So understand you are trading reliability for speed with these cars.