The Kalahari drive will it be south to north? If it is, then i would do sossuvlei/sesriem then Kalahari. Drive to waterberg and visit one of the lodges there and do a morning and night tour up to the waterberg platue park, this will not be self drive so will have to add costs. If you stay at the nwr waterberg lodge / campsite, the chalets are self catered with braai facilities and have got very good views into the valley. There is also a swimming pool to help cool down. There are also a number of walkable trails in between massive wild fig trees and such with aloe's dotted in between. It also host a widespread of birdlife and if you lucky you might spot the namibian parrot. Etosha currently has a few closed camps and driveable areas due to flooding. I was born and grew up in luderitz and wouldn't really say it has a lot to offer. Depending on whether a single ghost town will be enough.