I did two weeks in So. Africa in December and sort of followed the same way you are going. Flew into Joburg, rented a car and drove through the Panorama Route through the Blyde River Canyon to a game reserve near Kruger. Flew back from there to Port Elizabeth and drove the Garden Route to Cape Town.
On the Joburg layover we did a Soweto Township tour, very interesting and jarring to see mansions of those who have moved up next to the original corrugated metal shacks, sometimes left in the front yards as a reminder of their past.
You don't need to go to Kruger to see animals, Addo Elephant Park is a national park with plenty of wildlife to see in Port Elizabeth. That town also has a nice drive on the East side along the coast.
The drive from Port Elizabeth goes to a town called Kynsna which also has a nice waterfront with shops and restaurants. You have to go to a place called the Heads which is the cliffs that form the entrance to the lagoon, you can also take a boat to the far side which has trails along the coast. There's also a lot of parks along the way you can pick and choose for hiking, parasailing, mountain biking etc.
The next town worth stopping is Hermanus which is one of the few places you can do whale watching on land ( we came out of season) also has a nice waterfront and is the beginning of wine country.
If you follow the coast to Cape Town you have to stop in Betty's Bay to see several thousand nesting penguins and then you will drive a spectacular coastline to the city. Otherwise you can also drive through the wine country.
In Cape Town we enjoyed a beach town suburb called Camps Bay. Loved it so much we are still thinking of getting a condo there.
The rand is weak and but we found it more advantageous to get our money from an ATM or CC than exchanging cash, which is the opposite advice I would give for Argentina which is where we just came back from.
Enjoy, the people are friendly, the dollar is strong, the food is good if rather simply prepared and the animals are too tame.
