yes the kruger is tarmacked roads, rather like longleat without the fences thats why the private reserves are a more 'real' safari experience. haven't safariied in pilanesburg but they do have the big 5 there.
the private reserves are more expensive but i'd prefer 2 or 3 days on one of these than a week in kruger as they are nearer to the kenya/tanzania thing. (have done both myself).
the palace is fabulous as long as you take into account its pretty much 'plastic' africa, not a very real experience
personally if you're heading for the garden route unless you've got 3 or 4 weeks to spare, i recommend to my clients an itinerary similair to this:
fly to cape town, have at least 5 days there, time to do robyn island, table mountain, teh markets, get out to the beach (can't remember the name but will look it up) where the penguins are people friendly and like to play.
then drive to somewhere like mossel bay (perfectly safe to drive IF you stay on the main roads and don't divert, make sure you have plenty of gas etc).
stay there a couple of nights, maybe whale watch
drive to knysna area, again a couple of days relaxing
there are private reserves along this area so you can enjoy the whole safari experience here, some specialise in, say, cheetahs or elephants but some are big 5 friendly
move on to port elizabeth or durban
you can fly home from here or perhaps then go to joburg, a city thats definitely advisable to stay in the tourist areas, the mining tours and the apartheid museum are def the things to do here.
Sun city is a further hour or sos flight or a road transfer of, i think, about 5 hours (can't remember to be honest as i slept!)
if strapped for time i'd drop Sun city altogether, its great but not worlds apart from the same experience as say animal kingdom lodge, has a man made beach and water stuff like typhoon lagoon but not as good, has casinos and entertainment but unless theres a really big name playing, i don't think its worth the extra time and expense and the beaches on the cape are fantastic anyway.
hope that helps