1) People have been debating that for about a millennium. Since human beings aren't capable of understanding the angelic realms -- we're not that smart -- it's an open question.

2) I don't know of any book on any one of the archangels, but I'd be glad if they existed. Anybody else?

3) Yes. If you can, see if you can get an image of him that you like, and use that as a focus for your prayers.