I just booked a National Geographic 10 day tour that only visits areas in Namibia. Looked all over the internet for various tour companies and did not want the exorbitant expense to do a totally privately curated trip by myself.
For Michelle de Antis, check out their website. If you only want Namibia, the Wonders of Namibia tour was what I wanted to do but they have other combination tours as well and the price is reasonable.
This tour starts and ends in Windhoek and you can fly on Qatar nonstop from Doha(after connecting from anywhere else they fly) into Windhoek and avoid the JNB airport altogether!
Since I live in the US, I wanted an escape from the dreary rain, possible snow so am going in late February-early March. I know it will be very hot and I am glad of it!
Although people say that game viewing is better in the Southern Hemisphere winter or dry season, I guess I have had incredible good fortune to see all of the Big Five-including black rhino in late January/early February! Even saw a pangolin on my last trip. Hoping to finally see cheetah on this trip even though 90+% of cheetah in Namibia are on private reserves I have heard. My first 2 safaris-one in winter, one in summer the very first animal I saw was a leopard each time!
So just go whenever you can. My perspective was that I did not really find it easier to see animals in their winter versus the summer as for me, many animals blend in a lot more with the fall colors, but that is just my experience.