I have seen situations where an ad hoc road association can work well.  Usually it is where there are only a few people involved, and they are friendly with each other and willing to contribute to the effort on a voluntary basis.  Often there are some people who are willing to contribute and others who are not, and those who do contribute are more or less okay with that.

But if it gets to a point where those few people who do pay can't keep up with the maintenance costs, and/or where those who do not contribute are taking a noticeable toll on the road and those who are paying see it as unfair, it may be time to try to establish a statutory road association.   A statutory association has several advantages, including a rough framework of rules (with a lot of flexibility), the ability to enforce payment of dues, some measure of liability protection and the authority to buy more, and limits on how much a property can be charged.

A great place to learn more about how a statutory association works is MARA's fall Conference.  See the Events tab of this website for details.  If you have people who are on the fence about forming one, I highly recommend they attend - or at least send a delegate to come back with information.

I'll leave your other questions for others to answer.