At the outset Lee, and this is the blunt God-forsaken truth, you don't have to know too much or be an accomplished dancer to become a dance instructor. However, I must add, that will also reflect on the kind of clientele you interest. I have seen many 'instructors' lacking proper technique and ignorant of even the syllabus figures, and it is pathetic to watch them both teach and dance. Dancing, I believe, is not one field where a good teacher can outweigh the drawbacks of a bad dancer with poor technique.
Secondly, not all teachers are certified, nor does one need to be certified to establish ones own business. Along the way, many studio owners and teachers take more private lessons and get their certifications. If this is what you would rather do, then you should start right away. But as someone said a little earlier, B-W is not the best area to set up shop. The competition is intense and there is a good chance your endeavor may not take off. A small midwest town on the other hand...
Regarding joining a chain, I personally would dissuade you against it. They often teach their own syllabi and require contracts that forbid you from teaching in that area (outside their studio) for a certain period of time after you quit.
Let me offer something positive amidst all this. Join a good private studio, learn at least the syllabus figures and their technique in the dances that you want to teach. Then join one of many studios looking for instructors. Easier said than done, I concede, but I consider it sound advice.
Good luck, and enjoy.
Sri.