OP, I would say you probably should get the highest certifications you can.
I am not a teaching pro, but I have hired teaching pros to help me. I go with word of mouth, of course. But I probably would not consider anyone who was not affiliated with one of the tennis clubs.
The reason is not snobbery or anything. It is just that if the person is with a club, I know that they have been checked out at least a little bit and I am probably not going to find myself chained in someone's basement. And if you aren't certified, you aren't going to be hired by a club.
Also, it is cold or raining here quite often. I need someone with indoor privileges. Again, that means someone who is certified and can teach at a facility.
That said, I do not know or ask or care whether any pro I have used is certified. In fact, if a pro used certification as a selling point, I would immediately be suspicious given that I consider it meaningless. If someone doesn't know how to feed or drill or play, I will notice this quickly regardless of certification status.
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-- Master Moonballer