Just a little note on the minimum amount of drivers in a team: the thing that makes endurance racing special is that you are in a team: you depend on people and people depend on you. In a team you are not only swapping the driver seat, but also trying to help your other teammates. This whole dependency is no longer there when you allow people to drive as one man teams. I don't doubt it is a real achievement racing 24h on your own, but how fun is it for the other contenders to race someone who just wants to make it to the finish? Also, a team with four people provides a fun event for 4 people, a team with one provides fun for only one person. As the capacity of the server is limited, I think one man teams should be invited only if no other teams are available.
Besides that, I think the organizers have a certain responsibility that people don't do crazy things that might hurt them. Sure, people choose to do it themselfs, but I really think they shouldn't be allowed to in a race. If they want to do it on their own, fine. If there are enough nutters, let them organize a race, but don't allow one man teams to a team race.