5 weeks will allow you to see a lot of NAM and BOT. If you search the HUBB you'll find several posts where I made some suggestions what to see in NAM.
The most interesting places to visit are (starting from the South) Fish River canyon, Luederitz (with Kolmanskop), Sossusvlei (campsite at Sesriem), Swakopmund, Spitzkoppe, Brandberg, Twyfelfontein, Epupa Falls.
Further east: Windhoek, Waterberg Plateau, Etosha Game Reserve.
Generally, motorbikes are not allowed in Game Reserves -> hungry cats.....
Same applies to BOT, except for the transit route through the Chobe NP.
75% of the roads in NAM are gravel roads, but usually well kept.
When riding from NAM to BOT an interesting suggestion would be to travel along the Caprivi Strip to Katima Mulilo, visit the Vic Falls in Zambia, return, and cross to BOT at Ngoma.
BOT isn't that interesting for bike riders - secondary roads are often very sandy, countryside is mostly flat as a pancake. The tourist destinations in BOT are the game reserves, because many campsites in the reserves are unfenced, meaning that elephants or cats can walk inbetween the tents
So, nothing for the faint-hearted ;o)
Keep in mind that July is deepest winter, so temperatures in the NAM highlands drop well below zero at night..... But in those months you should always find a spot to pitch your tent. As mentioned above, in the game reserves you should book ahead. For the game reserves you could think about renting a car or pickup for a couple of days, but this should be bokked well ahead too, because many people from Europe visit NAM during the european summer holidays.....