First, welcome Rogue-Metalsmith! Regarding your vehicle questions, there are many factors, such as the type of vehicles, typical distances travelled, type of terrain travelled, etc. In our case here, we have two four wheel drive SUV's, 3 motorcycles, one with a sidecar, a couple of tractors, and lastly a velomobile and a quadracycle. Redundancy is good.
I would say a convoy would be safer, if all the vehicle occupants are armed, since the group could potentially lay down a tremendous amount of firepower, depending upon how they're armed. If the event of a vehicle breakdown, repairs could be effected while the rest of the group provides security protection. If a vehicle is not repairable, then the occupants and goods of the disabled vehicle could be redistributed to the other vehicles.