I travelled independently and I don't drive. Most say self drive (they drive on the left, by the way). It's a personal preference. The Baz Bus runs from Cape Town to Port Elizabeth in a day - both directions. It's basically door-to-door with hostels and hotels. It saves time, rather than finding you way from a bus station to wherever you're staying. Not a tour, but they do offer them. You choose where you're going to stop (along their route) and how long you'll stay. I did use their tour for the Cape Peninsula.
To do the Garden Route in a day would be spending the whole day on the road. I hopped along it over several days.
In Cape Town, I stayed in Green Point. It's a short walk down to the waterfront. I never felt like I was in a dodgy area around there when I was out after dark. Party people tend to stay on Long Street. Things do tend to happen to heavy drinkers, so if you're going out for the piss take some company. Always check with your accommodation about the local no-go areas, if there are any.
Robbin Island tends to sell out. They have a website so you can see what days are available. I lucked out, seeing a day with tickets unsold, walked down an hour before departure and nabbed a ticket. Excellent tour. If you're going walk-about, Bo Kapp, the Muslim enclave is nice to walk through.
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