What's the surf like?
Very consistent surf, world class surf waves, pretty uncrowded, sometimes sharky...
As far as surf goes, make sure to visit all of the traditional spots (Cape Town, Garden Route, J-Bay, Durban (no sharks in durbs)) but also not to miss some of the less-frequented areas such as the Transkei/Wild Coast. Be careful whose advice you take - many of the surfers are (unfortunately) paranoid. Explore (with care) the country and breaks for yourself.
South Africa for the most part is warm as the tropical east African current comes down the coast. From Richards bay down to cape Infanta (150km east of CPT) you could get away with a rash vest. Cape Town is permanently wetsuit territory though you could hack it with a summer suit for about an hour.