Exceptionally long distances to cover, needs some planning with countries not being stable as in yesteryear.
Friends with 4 x 4 vehicles traveled up in a group through Namibia, into Botswana down via Falls through Zimbabwe back to Durban. Valuable tips given was to travel with some goods to barter for food. In goods they referred to books for schooling, shoes, clothing, they had a clear run all the way through.