I stayed at the Hilton, the staff was very helpful and great! As for you excursions, I would suggest if you would like see Robbens Island, you should pre-book that one, as it tends to sell out fast.
I arranged all my excursions before I left with Rhino Africa. But I was traveling by myself and I wanted to research the company before I booked anything. But on my trips, several others mentioned they booked theirs the day before.
I agree with worldiswide, you can do a lot of stuff on your own, especially if you are renting a car.
Happy travels.