The factory spring rates are quite a bit lower than what come standard on coilovers (at least some coilovers - maybe the more pricey ones will have more purpose-designed spring rates?). According to DSE the factory spring rates are as follows (lbs/inch):
V6: Front = 145; Rear = 300
V8 (non Z/28): Front = 156; Rear = 383
Believe Z/28 rates are 305/610, but I'm not sure if that's correct.
BC Racing's BR series comes with 8kg front/12kg rear which is equivalent to 448/672, so considerably higher than the factory springs.
Regarding other suspension mods, the rear sway bar was changed to a new design in 2012 (mounts to the lower control arm outside of the springs rather than inside), so this won't directly fit a 2010/2011, and instead you'll need the 2012 - 2015 lower control arms (and sway bar links) if you want the new style (makes a huge difference). Also note that most bars including all of the factory bars will interfere with the V6 rear brake calipers; I have the JPSS bar (no longer made), and I've read the Hotchkis bar works too.
Besides that, coilovers/shocks/springs, control arms, bushings, camber plates, etc. are all compatible with V6 and V8 models. Believe there is an inconsistency with the 2012+ front bar and the 2010/2011 models, and the newer sway bar links have 12mm studs vs 10mm, but that just requires a drill (or something to that effect, kinda forget, might wanna do a search on the forum).
As for a subframe brace, JusticePete (former Camaro suspension guru on this forum and the (former) owner of JPSS)) always said that the solid subframe bushings gave the same benefits of a brace without the extra weight.
An angle kit if you want to call it that can be bought from DSE (
https://www.detroitspeed.com/product...parts/031730DS), otherwise you'll have enough camber/toe adjustability from the factory for standard street driving, assuming you don't lower more than 1 - 1.5". Camber plates can be used to move the whole strut inward, increasing angle of inclination and thus improve straight line stability and wheel-centering exiting turns (again, overkill for street driving).