If you are going to do a BBK, I would go with StopTech. I am sure all the makers do some testing, but StopTech publishes there testing and makes it really clear what they do. For example, they do J-turn testing, endurance testing, stopping distance, and many other tests. They really do find the perfect setup (caliper type and rotor size) for every car.
Speaking of which, if you do a front-only BBK, then you need to take some precautions with the rear brakes. Stoptech and many others know that the front-only BBK will transfer more braking force to the rear rotors. This is by design, but it causes the rear pads to burn up much faster, especially if they are stock. Member Enthuz (Bruce) torched a set of Carbotech Panthers on the rear in one track session because of his front-only Stoptech kit. Later, he found out how to reduce this issue. First, run a better than stock pad in the rear. Second, they burn up because of heat. Removing the heat/dust shield from the rear rotors will help to control the heat, extend pad life, and it has no side-effects.
As for the staged upgrades, they are great. A caliper upgrade would be nice but the cost would likely be similar to a BBK. You could always get a StopTech stage 2 kit and buy a set of used track model Brembo calipers. However, you would have to buy the track model Stage 2 kit and the new calipers at the same time. Or at least, you would have to mount them at the same time. You cannot run the regular Stage 2 rotors with the track model Brembo calipers. The rotors are different sizes.
