Someone happens to be the ultra-competent know-it-all, and they really do know it all ? Many want to make that individual the Great Super Boss for Life ? You can always give such a person a special role appointed by the central council, and so the power is retained in the people to prevent future tyranny.
1. Bigger groups:
In the larger model there is another layer there, but only one, and that is enough to handle an entire nation of 20 million persons. That layer is achieved by capping the sub-group mentioned above at 50. That yields you perhaps thousands upon thousands of these delegates, who then together are this 'ruling council.' But that is too big to be practical and therefore you divide those delegates again into 50 groups and they again elect a representative. Smaller more local councils can also be created in the same ways by these delegates. It is a simple idea, now that you know you might perhaps always remember it. You can now organize a group of any size. The idea is that the delegates can be replaced at any moment, so the power stays at the base.
2. Economics:
Long term survival situations (years, decades, eternity) Farming: Make equal valueable plots for gardening for everyone, and give people the exclusive use right over them. Establish this as a right for all, to have the same amount of soil value as the others within that 'nation.' This may require repartitioning sometimes. Establish a trade economy, people trade according their own will. Not a totalitarian plan economy, except if the group is very small like 10 persons or some more.
With these things going, you may have set up a mini-society that could work and solve more problems for themselves later. Money, social relations, housing, laws and bylaws, these could all be done later as the needs arise and could be issues beyond immediate survial issues. Good luck.