The next step would be a DFA, Doctorate in Fine Arts. (this has until recently been only an honorary degree gevin to people who excel in the fine arts for example Stephen Colbert and George Strait both have them.) Some schools are now creating DFA programs. Youd have to hunt for the ones who do. Then some schools are also now making PhD programs. You would have to find the schools that offer these programs. However it would be a benefit because then you have a leg up on everyone w/ a MFA. However you could teach at a collegate level with an MFA for it is still considered a terminal degree.

If you want a full-time faculty job, you will do far better with a Ph.D. If you are looking at an occasional part-time teaching job, you might be okay with the MFA (although given the competition in English, that may no longer be the case for long).

Take a look at some job listings to get a better sense of the requirements, but you should be all right with just the MFA. Publication credits help, too.