Three weeks is a long time in Kruger. Most of the park is the same landscape and vegetation. Sabi area has the best game viewing. I'd probably them hop across to one of the other Singita lodges on the east side of the park. The north is very cool and quite different to the south. Wildlife isn't as prolific though but bird-life and vegetation differs quite a bit (eg more baobab trees which you don't really see in the south). The Outpost Lodge is okay, not luxury when compared to the big guns further south though. But okay to spend a couple of days. To be honest, I'd be bored after a week in Kruger (I spent six days). I'd split three days in Sabi area, three in the another Singita in the east and then three up north. Driving is easy inside the park. You could probably throw in Ngala if you wanted to break the drive north and add some more time.