Yes you shoulid absolutely go to the Delta in Botswana rather than South Africa for your Safari. There is lots of Botswana vs South Africa safari debate in the Africa forum. A water based and a land based camp however is a good combination.

Re Stellenbosch it is pretty and worth visiting, but it is not far (1hour max) from Cape Town. I stayed in Cape Town at the One & Only which I would highly recommend, and the O&O had access to chauffeur driven mercedes cars for private tours which made going to places like Stellenbosch very easy from a Cape Town hotel.