hi there,
congrats on your upcoming wedding. I was in sa for my honeymoon last june. We hired a car for two days in Capetown, to do the drive to the cape of good hope - which was fantastic. We also drove to the winelands on the second day which was great. We spent 5 days in Capetown in total and the other 3 days we didn't need a car as 1 day was spent up on table mountain (the hotel staff drove us - 5 min spin), another day we went shark diving , where we were picked up in a minibus. The third day was spent on the waterfront and robben island, so we didn't really need a car.
As far as i remember, the hotel staff booked the car for us. It included insurance, mileage etc. we paid for the petrol ourselves. The roads over there are great and its very easy to find your way around.
Hope this is helpful - wish i was going back...
Milly