First you will not need all your required certifications and insurance there.
The best bet would be to apply with a hotel group with spa facilities. Do not expect to get a huge salary though.
To give you an idea of salaries.
A top hotel Manger and his wife both working in the hotel live in situation only gets $2000-3000 per month if they are real tops .
Your position will be considered much lower, so much much less income there.

However there will be tips from international tourists too.

Most expats prefer the locals for treatments because they are so dirt cheap!

Another option would be to enter as an investor and start your own business.

That would require a substantial amount of cash upfront. I will send you the link for Tanzanian Visa Services .Overseas Embassies and Consulates of Tanzania