[Mr.ac]

Welcome.

Well, to answer your first question, depends how far gone your rear brake are. If they are ready for replacing then go on ahead.
Or, if you got the money to spend, get it. There is really no wrong answer to that question.

Yes they work fine on stock rotors.

Yes you should bead them properly. Yes they will still be noisy. That's the nature of the beast when it comes to high performance brakes.

Now, that being said if all of your driving is 98% on streets, and 2% is on a race track, then these pads are not meant for you. You might want a notch lower or just deal with the added noise. It's up to you.