Many thanks to Chris Card for all your wise and useful advice!
There are incredible sights to see and lots of good places to stay: campsites and lodges. Book them in advance in the holiday periods, particularly in Etosha. The remote areas should be taken seriously though. Some of the routes through Kaokoland are extremely tough going and a breakdown of any sort could see you stranded for days. There is no cell coverage there so take a satphone if you are on your own. Plan your routes carefully and don't leave it until the last minute to get fuel - the next pumps could be many hours away. Be aware that what doesn't seem that far on the map could be a lot slower if the gravel road is badly corrugated, or barely there at all. Don't drive at night if you can possibly avoid it; you can't see the road surface clearly or the animals getting ready to spring out in front of you. The advice we were given in Opuwo (and took) was that it's better to try to camp near other people if you can't reach your destination, and get their permission first.
What to bring from home...
The Tracks4Africa Namibia map - excellent detail.
A Garmin satnav with the T4A Namibia road map installed. We simply could not have reached some places without it.
Really good sleeping bags - the nights can be very cold in the winter.
Several multi-LED lights/head torches to hang from tent roofs and over food prep and cooking areas. It gets dark quickly!
Gaffer tape - for just about anything that needs a quick fix.
Multi-tool or penknife for can-openers and scissors and bottle tops and small repairs.
A folding washing up bowl is brilliant
Two thick tea-towels for lifting hot pans from the fire as well as drying up.
A small tyre pressure gauge for checking tyres and getting the right pressure for the road.
My wife says a "she-wee" is a must
A good solar charger (at least 15 watts) with a big battery is good for gizmos.
Take spare camera batteries and big memory cards. Everything is a photo-op