Visa: Nearly killed us but got in London before departure. they are apparently available in Bamako. We had 3 months to get the border and made it by the skin of our teeth. 200 USD each!
Insurance: Carte Rose
Diesel: Can be difficult to get. 40 N if you can be bothered to queue for hours/days.. 120 N otherwise, fluctuates a lot.
Police: A lot of checkpoints, up to 20 a day. When crossing the border from Benin, they didn't wear uniform and tried to throw nails under the car if you didn't stop. No bribes paid.
We stayed in hotels for 4 nights as we drove across.
Drill Lodge - Camping for 4000N 7 hours north of Calabar. A real treat of a place.