Quick brake question. As long as you replace rotors and pads in pairs (front/rear), they don't have to be matched right? Like you can have high performance rotors with premium pads in the front and have generic rotors/pads in the back, right?

Shouldn't be a problem as long as you do them side to side like you said.

 

I put ceramic pads and cryogenic rotors on the fronts until I had the $$ to upgrade the backs.

Yes, you can do one axle (front or rear) at a time if you need to. I'd certainly recommend doing the front first.