That's an open question. From what I've heard, they're going to go with "Mrs. King" for Camilla. Perhaps they'll make her Princess Consort, as Phillip is Prince Consort to Elizabeth.
Nope, not for at least a century. The Crown can be regulated by Parliament. Mostly, folk are just trying to politely avoid the issues.
Probably. It would have been a huge breach of royal protocol, but there was no civil or ecclesiastical legal bar to Ed marrying Wally.
Nope. The key is that Charles committed adultery with Camilla. That makes her off-limits permanently, as regards a marriage legitimate in the eyes of the Church of England.
The problem is that one of the titles of the monarch is Defender of the Faith. She is the head of the CoE. Kinda awkward when the head of the church is in a marriage the church doesn't recognize. I suppose ecclesiastically, Camilla's just some bint Chuck sleeps with.