I guess you need to ask yourself at what level you want to teach. If you want to have a tenured position at a higher level institution you will need the MFA.

As someone else mentioned many community colleges and smaller private colleges need instructors and usually require less initial background. Such institutions are usually more flexible in how courses are taught by the instructor. You can also teach at different institutions. I have a friend who owns a business but with a background in meteorology and physics teaches courses part-time a the local community college and a priviate school. You could also teach the occasional workshop.

One thing to keep in mind when persuing an MFA and PHD is that you basically have to tow the party line and kiss a lot of ass to get through the process easily. Most professors have their own ideas and theories about your chossen profession and they are going to try to get you to adapt their views. You will have to play along to achieve your goals, especially when dealing with thesis advisors or committees.

I personally would explore teaching on the community college level first and see if I enjoy teaching in a academic framework.