Peter knows this place well. You can use the Spots menu on this forum to check out the various places, but Witsands is easy to find, just north of the village of Misty Cliffs (entirely private), which in turn is just north of the village of Scarborough (three nice cafes here for lunch if you don't bring something along). As you can see from Kevin Langaree's latest vlog, you park along the road above the beach and walk down. And as Peter says, if you are desperate to kite all day and Bloubergstrand is still or SW, you can start at Platboom mid-morning, move to Witsand early afternoon, and end the day at Kite Beach or anywhere along Bloubergstrand, or further north if into waves, like Haakgat. If going to Platboom, most days are not too busy, but weekends are very busy just getting into the park, so you have to get there early (plus it is a bit pricy for non-South Africans, so there will never be a crowd there). But sometimes it blows all night and into the morning, so the truly addicted will grab a morning session along Bloubergstrand, which will be deserted. But I'm too old for that, I need some recovery time each morning.
No way to guarantee moderate waves, just check the forecasts at Windguru and WindAlert. The waves here, like the wind, have a lot of power in them and when over 3m need respect, either jump over them if you are confident of your ability to do that right every single time (getting it wrong would be painful), or chicken gybe away. The only problem with the latter is if the beach is crowded you might tangle with someone heading out behind you, but mostly it will be obvious to anyone behind you that you are not comfortable and they will avoid you. If the waves are too much for you, check the forecast for Langebaan where you have two flat water choices, but it is 1.5 hour drive from Cape Town. Inbetween are a few more waves spots, like Melkbostrand and Yserfontein that Peter mentions, but again like Platboom you will have those largely to yourself. Even more adventurous types can go further north than Langebaan, like Paternoster, for waves, but I've yet to do that - I think this Langaree vlog is from there, but you need to know what you are doing and it's a long drive.
And of course for strong SW or even westerlies, head to Hermanus like two of Kevin's vlogs this season, or if completely dead at Cape Town look for the easterlies to have moved further east to Struisbaai near Cape Agulhas for waves or the other Witsand on the Breede River mouth, famous for flat water on the lagoon but the waves can also be fun, albeit onshore wind direction, or even Stillbaai further east. And if you have time, there is the rest of the coast all the way to East London and beyond. Spots is your friend for each site.
Every now and then we might get a strong NW flow, although I don't think there will be many of those after the New Year, but that works well all along Bloubergstrand and further north, as well as all the way down south at Platboom.