M. Scott Chambers
The only advice I think I'm qualified to give is this: don't write for any reason other than you enjoy it. Statistics tell us we're not likely to become fabulously wealthy. Writing and getting a book published is far too much work if you don't actually enjoy the creative process. There are a lot of easier and more efficient ways to make a buck than writing. (There are, however, few that are as much fun.)
That said, if this is what cranks your engine, write away!