Hey Dom,
So, when you get to Johannesburg, you are (relatively) close to Waterval Boven which has beautiful rock and more bolted routes than most people on this forum can count
Very good roads from Joh'burg to 'Boven, whether going with your own transport, or by bus.
For busses: check our city bug, greyhound, (and there are others)
You can either camp at Tranquilitas, or stay in the backpackers in town.
The friendly people from roc 'n rope
http://www.rocrope.co.za/ can give you plenty info.
The Gauteng locals can also tell you about other bolted crags close to Johburg, and if you hook up with the MCSA you could maybe join them in the Magaliesberg (some bolted, but mostly trad).
If you plan a boven trip, lemme know. We could hook up, or I could get you in touch with others climbing there.