1 - no; those rings have to be ordered from the Guardians of the Universe, and the waiting time can be a year and a half or more
2 - phosphorus, sulfur, arsenic, and antimony
3 - no
4 - I don't wear them, I would tend to think that they would actually hinder technique
Seriously though, when you watch these upright guys, the way they position their left hands when playing way up the neck, I can see where having a ring on one those fingers might, for some, be a bit in the way.