I covered 6,000KM over 3 weeks in SA and for the best part driving is as you would expect back in the UK. I did not experiance any trouble.
I was 22 when I hired, I used firstcarrental.co.za and got a stupid good deal on a 3 series. You
will, I repeat
WILL need
TWO CREDIT CARDS to hire in SA. This is non-negotiable. I spent a week on the phone and emailing MANY MANY companies trying to get around this (My credit card from the bank was delayed and I might only have 1 card available) I talked with managers, supervisors and anyone I could and you will not hire without 2, do not even try to turn up with 1.
There ARE speed cameras and you WILL get fined, but the fines are small. I had 10 of them follow me home, forwarded onto me by the hire company.
I stopped at all traffic lights at all times of the night, but would not hesitate to floor it if I felt I needed to.
I got stuck behind a lorry which was suicidal, overtaking traffic on the inside in closed lanes of dual carriageways (road works) knocking downs 10s and 10s of signs, bollards and cones etc. Pretty damn strange. Got stuck behind a pickup full of natives in the back. Was VERY VERY dodgy and I did not overtake it as when I made a gesture that I was going to they swerved into the road.
Keep all valuables under seats/in the boot and not on-top of seats etc. Thieves will smash windows and grab whatever they can.
Got stopped in a few road blocks, once by a white South African with a shotgun who decided he did not need to see my ID after seeing I was white and British

In a regular check or two but never got pulled over.
They have an equivalent of the hard shoulder. Lorries and slow moving vehicles often straddle it to let people overtake more easily. BE AWARE they are not present all of the time and they can stop so be prepared for vehicles using it to move back into the lane fully. If you have inpatient/maniac drivers behind you, feel free to use it to let them get past.
Do not risk any overtakes, even if you think you can make it. There are maniacs who will overtake you while you are overtaking (and my increase your overtake time) and maniacs who will overtake on blind crests and corners.
MOST fuel stations will NOT take cards, keep cash handy for fuel. It's rare you will find a station that will take cards for fuel. Speaking of which, know your fuelling points. You may have distances of 100s of KM before the next one on the N1 for example.
Flashing hazards after an overtake and tipping attendants is not required, but almost everyone does. I suggest you do or you might have an angry trucker coming at you
Roadside Parking - You can not park contraflow. You must park facing the direction of the sides travel.
If I think of anything else I will add it!