I’d put the max closer to 150 myself, I think 200 would be pushing it. Though it does give me an excuse to discuss a sort of thought-game some friends and I have been playing.
The idea centers around a core/cluster seastead arrangement. The basic idea is a large seastead city cluster built of smaller core groups. For instance a closenit group of spars with a total of 125-150 citizens would constitute Core A, then we have two other groups(Core B and Core C respectively) that are separated from one another(anywhere from a few dozen yards to a few miles). Each would be individual communities but they work in tandem to form a cluster leading to increased security, production, etc.
Our thought game is to basically each take a Core and design it with different social attitudes and then discuss how they could function in a Cluster.
The reason we can handle more than the direct neocortex size formula might suggest, I personally believe, is because we have a certain amount of transitive trust, that we can communicate through words as well as actions. If you vouch for me in your society, then the risk in accepting an outsider is lowered.
Even in a tribe of 150 people, or a military unit, or whatever other organization, not everybody knows everyone else equally well. In fact, they probably overestimate how well they know most of them, but they have facial recognition and tribal identity, which makes them a fairly safe bet to turn your back on. But in each of those organizations, there are usually many connectors to other organizations.
You and I might belong to a country club together, and that social circle is part of each of our “tribe”. But we work at different places, so that part of MY ‘tribe’ doesn’t overlap with yours. I have about the same number of relationships as you do, and we identify largely with each other, but our 150 people are the same for both of us. Even if we lived and worked and socialized together all the time (say on a Seastead), my specialized trade may have outside connections different than your trade’s outside connections and we form attachments to different people outside the nuclear group.
Thus, when I’m positing a max number, I’m talking about permanent residents: some people will come and go, and form very close personal attachments and working relationships with some of the people on the Seastead and be hardly known to others. In terms of totals, it probably scales up to at least 300-500 people before it really becomes necessary to formally codify most rules and laws, because the people who come and go will have very similar values in regards to the important things, like fouling your home, basic humans rights such as the right to one’s person and property, common courtesy etc., and this is applicable to your idea of clusters of smaller communities.