Ratings
I would say for Botswana, a C172, C206, Airvan GA8 or C208 are all good ratings to have.
You need 500 Hours to get a work visa here, so that's the minimum. There is quite a big drive to get local pilots flying and no longer have expat pilots.
An instrument rating is need for the company's insurance although all the flying you will be doing is VFR.
If you have the money to do a Bush flying course, go for it!