Some good advice above. As someone said, for a route check with an overland company, when I drove for one we were always up to date with political situations and stayed flexible enough to change en route if required. You will meet other travellers, not so much on the road as at the classic resting spots - good secure campsites generally where folk stop and do maintenance and drink lots of cold . With a British passport (and several others) you can get visas en route generally though I would recommend getting at least the Nigerian one before setting off, it's never the easiest.
In west Africa I think Mali is one of the best countries. The drive in from the border in the west can be brilliant if you get the route right - vague tracks through wee villages for a few days until you intersect the north south dirt road. Tombuktoo is worth it if safe at the time. Gabon is great, Ouagadougou is good even if only because it's a grand name!, Northern Cameroon is fine. The east and south of Africa are well known and full of travellers - I reckon it's better to turn around in Cameroon and take a different route back north!
Lots of great spots that will only be great when you get there. You shouldn't go too much on recommendations as the trip will make itself once you get going. Enjoy.