Hi I took the 5000 rand and withdrew another 5000 rand from an ATM while there, which covered me comfortably for spending and payment for all the optional excursions. Credit cards are readily acceptable, but as Olly said let your local branch and your credit card provider know you are travelling. One woman had a Visa debit card, which did not work in the ATM, despite her informing her bank, so it's a good idea to have more than one source of available money if possible. By the way, no one was asked any questions about how much money we took into the country, so we could have easily taken more but I don't want to advise this in case you have a different experience! I don't think there is much point in taking sterling as the excursions have to be paid in rand - it would be easier just to use an ATM and we had numerous opportunities to use one - just don't go alone, as there is a cloning scam going on and you may be hassled or worse if you go alone!!
Hope you have a fantastic holiday, I did!
All the best,
Bob