Yes, I believe this was stated on the JoS site to be the case.
Now, I am not 100% sure on this, but I think this effect may be amplified if you use actual gemstones on your rosary, as opposed to plastic or wood. I could be wrong here though.
Yes, so it’s ideal to have one for black magic and one for white. So the energies don’t fight each other. Also it’s a good idea to store them in a particular place, like a box or silk bag. Something to hold them in where the energy won’t leak.
Anything you use steadily will build in energy, whether meditating and doing workings or not. You’re bedroom or places you spend time a lot in will have your energy. Precious items you use frequently, etc