Any suggestions?

The itinerary as of now:

Land in J-burg - go somewhere east and stay the night on the way to Kruger
3 nights in Kruger (already have cabins booked).
1 night somewhere in either Swaziland or on the road to Durban
2 nights in Durban
2 night in Golden Gate Highlands NP (near Lesotho)
1 night in J-burg
Fly to Victoria Falls - stay 3 nights (guessing Zambia side)
Fly to Cape Town - stay 5 nights

Now, the first part of the trip is relying heavily on a lot of driving (4 hrs + 8 hours + another 4 hours + another 4 hours). But, I don't mind driving. We have a VRBO booked in Cape Town near the waterfront as well as a rental car there.

What are some must-sees along the way? Random suggestions that may help us?

Driving in south africa sucks. It'll take you a lot longer than you expect.

Driving in SA is very sucky! in Cape Town Table Mountain is a must, hopefully it will be a clear day and you will have amazing views of the city. Momma Africa for dinner if you want to try a variety of wild game. You might need reservations, I am not sure. Vic Falls you might want to hike to the devil's pool ( I think that is what its called) or if your adventurous you can bungee jump off the bridge. I did it and was quite the adrenaline rush. Enjoy your trip and take a camera with great zoom and plenty of memory cards!

Like others said, driving long distances in SA is awful. Small roads and lots of people walking on the side.

Cape town is freaking awesome! If you're there for 5 days, make sure you spend a day going shark cage diving if the weather is nice. It rained when we went so we couldn't go, but I really regret it.

As far as driving goes - we are somewhat prepared. I have talked to someone over there already with regards to roads and what to expect. I am avoiding driving at night for my own sanity. I am also staying only on major roads (except for some minor trips off of them).

Victoria Falls - Skydiving and lion petting thing are both on the agenda
Durban/CT - talk of shark cages have happened.

I second Table Mountain and Momma Afrca in Capetown

In addition to what was said for Cape Town, Cape of Good Hope is a nice scenic drive and view. If you're into wine, you can go to the Stellenbosch region. Robben Island off the coast of Cape Town is very moving as well. That's where Mandela was imprisioned.

You'll be surprised at what a major road is at times. The "interstate" highways sometimes become one lane roads in the small towns.

I had friends, girls, take the train from J'Burg to Victoria Falls in Zimbabwe which I thought was the best visual. Not sure about the costs in Zimbabwe as some parts of Africa are really high.