Well, in all three questions I can answer you identically.
I'm a journalist specialized in this type of musical media and specifically, Rock and Heavy Metal.
On the source, say that both me and fellow professionals, we have several sources among them, fan clubs, management agencies, our questions in interviews and also sometimes, the musicians themselves.
Another thing that helps a lot, is to play songs well and be knowledgeable about them...
Personally, I'm a big fan of Iron Maiden and, as such, when I do an interview I know what to ask what a fan would like to know.