You have a couple of options...
Cape Town/langgebaan - Wind is pretty consistent now, with most guys using 7m (projected size, not surface area) around this time of year. Water temperature is cold, but the wind is definitely the best in the country. Langgebaan is definitely the smaller town you are looking for so check out capesport.co.za for details on that. Be wary, this place can start getting really busy this time of year.
Durban - Much warmer. More of a 8.4m projected size this time of year but bring an 11.8m for the softer winds. Water temp is around 25 degree's C so wetsuit not required. Go to http://www.windsurf.co.za
and email richard if you need details or shaun at http://www.tsunami.co.za
There are some smaller towns but those are pretty much the main ones.
Also go to http://www.kitesurf.co.za
the unofficial SA website where you should be able to post any queries. Alternatively, email me and I will send you email details of all the guys you need to get hold of for accommodation etc.