I grew up in Cape Town but only started kiting once I came to Perth, and have since only kited a few times there when I've been back. The wind is awesome, but of course there was a dead spell over Xmas last year when I was there with all my gear (damn you wind gods).
Location wise, the beaches in Table Bay have already been mentioned, but other places to check out are Kommetjie, Scarborough and Muizenburg (haven't ridden at these spots but have heard good reports). Langebaan holds a massive downwind race every year, with a few hundred kiters and polies participating (not sure of the exact date) which might be a fun thing to try.
At Blouberg, in front of the KFC and the Best store, there's a guy called Bobo who for a nominal fee (10 South African rand or about a buck fifty aussie) will pump up your kite, launch you and catch you when you come in.
I would be wary of leaving stuff on the beach as it might grow legs and I would definitely get a waterproof pouch to keep my car keys in while out on the water. Also never leave anything visible in the car when its locked up and you should be all good (same advice I'd give to anyone kiting at Leighton).
If you're looking to get new gear, you can pick it up brand new in Cape Town for a sizeable discount on Aussie prices (and yes I know I'm opening a can of worms by saying so, but it is true) particularly on the higher end stuff.
There's lots of accommodation around, but you might well have to wrestle a few Euros to get some as the place is crawling with them in the windy season. I'd recommend trying to find something at Big Bay (that's the spot where Len10 was throwing those mega loops a few years back).
PM me if you've got any questions
Below is a picture of Xmas eve last year when a storm front pushed some big swell and big winds through, and the other one was a nice sunny day in January
) where summer water temps are 8-9oC (colder water in summer I believe due to warmer winter currents) - bloody freezing!! 
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