Sunset Beach is popular for kitesurfing between November and March, with the most consistent wind coming between December and February. During these months you can expect between 10-40 knots depending on the day, so keep your eyes on the forecast, and watch for the table cloth (the clouds) over Table Mountain. The wind here generally starts a little lighter in the morning and then picks up a little later, so morning kite sessions tend to be more relaxing, while afternoon it gets busier and the kitesurfing conditions get more hardcore.
The beach is wide and sandy regardless of the tide, and the waves are generally small to medium in the morning, maybe getting a bit larger in the afternoon. When the wind gets really strong the waves can become a bit of a mess, and the spots further downwind might be a better option.