Here is a good article, by Doug Menuez , about balancing what makes you happy in photography and paying the bills.

http://www.editorialphoto.com/articles/doug_menuez/

“To learn about longevity, it’s instructive to look at the great masters - pick any that inspired you in your early career or education. I doubt they thought consciously about having long careers. Instead they instinctively made choices that guaranteed that to happen. They were true to themselves from day one.”