I want to get a visa for Tanzania, Africa. I am planning on working there and hopefully stay there. But I think the only visa I can get is a visitor visa. So if I leave every 3 months, how long do I have to wait before returning?

3 May 2018 update:
I have been here a few months now, and want to clarify that I work in the medical field via the internet with the US. I don't work here in Tanzania, I do plan on starting a business at some point and will do it the legal way, get registered and get the correct type of visa. I apologize for my ignorance and now know the process.