I'm going to South-Africa at the end of July, and up to Namibia, Botswana, Zambia and back to SA. Starting in Capetown.
You have picked the 4 best countries in Sub Saharan Africa.
South Africa and Namibia are the best, Botswana you may have a bit of Cop hassels but it is still OK.
Zambia I was in in March and I had an amazing time, no hassels with cops and the people are great.
I live in Cape Town BTW.......... en daar woon baie Kaas Koppe hier so