Hi darinm81! Welcome to the forums.
You have found THE place to find out more about your KNP holiday!
The South would also be my choice for the 5 days. 2 nights at 2 different camps.
This way you can experience two different camps.
Berg en Dal and Lower Sabie sounds like two good choices to me - but hey - you can choose any camp in the South - they're all great! Availability might be the guide in the end...
Driving from JHB to Malelane Gate will take you 4-5 hours.
As mentioned - door-to-door, the flight will probably take you just as long or longer.
Driving the N4, especially via the Schoemanskloof side, can be quite beautiful through Mpumalanga.
There are nice shops and places one can stop on the way - but I won't do too much of that - Kruger will be awaiting you! It is a good road.
Driving in KNP is lovely.
We usually go on a morning drive - out early, drive around, make breakfast in a gas braai/cooker which you can rent at a picnic site, drive a little more, then back to camp for an afternoon nap (especially over the hottest part of the day, when all the animals are hiding in the shade as well).
Then out again late afternoon for a 2-3 hour drive.
As already suggested - you can buy a Kruger Map-book on arrival at the park and plan from there.
Most camps have sightings boards - where people indicate where they have seen nice sightings during the day.
Look at them to get an idea as to which roads are "hot" with sightings.
And talk to other people.
Especially if you see someone whose car has a yellow ribbon tied to it.
That means they're on these forums, very friendly
and will love to share their sightings with you!
Remember to get antimalarial tablets from your doctor - it is peak season for malaria in Kruger. Unfortunately - he/she will not be able to give you an antidote to the serious addiction you will most likely develop to Kruger...