You probably will have to choose fewer countries.
We did the following in six weeks without much rush:
We went from Cape Town to Livingstone, Zambia but only visited Windhoek, Sossusvlei, Etosha, NKwazi, and Ngepi in Namibia, Kasane in Botswana, and the Victoria Falls from Livingstone in Zambia.
With a car this is more easily doable though the journey from Cape Town to Windhoek, and Windhoek to Etosha are long ones. And you would have to rent from a company that allows drop off in Livingstone. Bound to be expensive but I have heard that it is possible.
Though we caught a ride on an empty overland truck from CT to Wndhk, one can travel fairly comfortably from Cape Town to Windhoek to Livingstone on Intercape Mainliner the SA bus company, but you will be spending hours on the bus. (Google it.)
In Windhoek we stayed at Backpackers Unite and rented a car for Sesriem, Sossusvlei. Backpackers Unite arranged a safe taxi for us to the informal transport area on the edge of town where we got a nice 30 passenger mini bus to Tsumeb. (We were the only tourists on board. Namibia requires everyone to have a seat we were told, but the seats are close together if you are big folk.) US State Department pages on Namibia says tourists in Windhoek have gotten robbed by taxi drivers they flagged down on the street, but the site has suggestions on the type of taxi to take.
In Tsumeb we stayed at Mousebird Backpackers Lodge Tsumeb, Namibia. We called them and they picked us up at the informal bus stop at a grocery store. In Tsumeb we rented a car for Etosha. Hired a taxi to Rundu to NKwazi, another scheduled taxi to Ngepi Camp at Bagani/Divundu.
Ngepi Camp gave us a ride out to the highway where we picked up the South African Intercape bus there on to Livingstone, Zambia (opposite Vic Falls.) The bus does not come everyday, so you have to schedule around it.
On other trips, we have gone from Ngepi Camp to Kasane in Chobe NP via Katima Mulilo by mini bus. One time we arrive just in time, another we had to overnight in Katima. From there taxi/ferry/taxi or shuttle on to Livingstone, Zambia (Victoria Falls).
British Airways and South African Air fly back to JNB and on to Cape Town from Livingstone, Zambia......
All the best!
