I believe the best legal structure for a community of like minded people would be a corporation. The corporation would be responsible for communication with the external world. As much as people might want to cut off the corrupt society around it is virtually impossible. The corporation could operate on property investment and management and would ideally generate just enough revenue to pay the necessary obligations to the outside world, buy materials and equipment not available internally. The corporation would have a minimum number of employees coming from the ranks of its shareholders the same people that form the community.
Let's take a hypothesis that a hundred families would form a community each buying equal share of the corporation that would give them right to claim a lot for their use in the area that the corporation would purchase. The lot selection would be on first come first served basis. Each lot would be about 5 acres divided into residential, production and forest or pasture areas. The area reserved for lots would be surrounded with a safety area of about a hundred yards and would be covered with thick vegetation and forest. The whole area would have only one guarded entry and exit point. With these conditions the required area would be just below 300 acres.
The community needs all kind of professionals in order to operate. All required professions would probably not be found and those services would have to be bought outside until such professional becomes available from inside. Business inside the community would work by competition, supply and demand. If there are too many people offering the same service the price of that service would go down until a balance is found. The shareholders have freedom to use their lot as they see best within a collectively agreed framework.
Business transactions between community members would normally be settled on a person to person basis. However, when the obligations become bigger a public notary service is needed to register the obligations and transactions. That would also be important in case one of the parties in an agreement dies or something unexpected happens.