Another thing to consider if you locate in an area where there's a high concentration of shops and instructors is you'll need to find some way to set yourself apart from the herd. Because I never taught to pay the bills, I was able to turn down those students who didn't want to spend 6 weeks training for open water. I could charge what was roughly double for advanced and specialties compared to others around me because I never taught to standards and left it at that. Always exceeded them and had requirements to earn every card. If that meant having to do an extra weekend of dives or an additional pool session, that's what it took.
You'll need to be able to explain in solid coherent terms why you teach the way you do and the difference it will make to your students.
I preferred not to teach basic open water. Advanced and specialty classes were more fun, took less time, and were much more profitable. I taught a private 5 day AN/DP class and the tuition and books alone was $1500 for the student. We shared lodging expenses and he paid for most of our dinners.
I took a week's vacation from work to do that class and got my vacation pay as well.
With the amounts I charged for something akin to advanced open water (425.00 per person, 650 for a private class) I didn't need to have more than the two students at a time max I taught.
If you don't do something to make your class standout, you'll have to charge what everyone else does and hope it's worth the time and effort you put in.