Hi,
1.- No problem using several piezos - retrigger settings etc are pretty normal, similar to pads with 1 piezo.
2.- Yes, I forgot to do it in the video, but the edge also functions as a choke.
3.- I don't own any branded cymbals so I couldn't really say. My guess is that they are probably a bit louder than a Roland or Yamaha rubber cymbal because they just have a 1mm layer of rubber on them. I suppose you could just use thicker rubber or more layers to reduce noise more. On the plus side, I like the feel a lot; they almost feel like an acoustic cymbal. I used to have an acoustic cymbal covered in EVA and rubber and hated the rubbery, spongy feel. What does tend to make a bit more noise is when you hit the bell, because of the plastic hitting plastic. I've thought of ways to get rid of that but to be honest it doesn't really bother me that much as I play with headphones and can barely hear it. The edge is quite silent. In the other thread where I posted about the previous version there is a video - in the second half of the video you can hear the ambient noise of the cymbal.