5x114.3 will NOT fit the Camaro. The proper lug nut holes are 5x120.
Not sure about offset for 19" wheels, but a lot of people are going with +35mm or +40mm offset on 20" wheels.
BTW, have you looked at wheels on Tirerack.com? They will have a list of 19" wheels that will work on the SS. I ordered my winter tires and 19" wheels from them recently and the wheels and tires look and fit great!
Hope that helps!
