Well spoken. Magic-number I've seen is 150 people in stable , pre-law self-governance. Worth noting you ended your point about mechanisms of group organization/decisions with Robert Rules of Order. That indeed was the gentlemanly place to stop.
But. It's not historically a correct endpoint for "societies". I believe the earliest attested cases are about 12,000 years old ( southern Egypt ? ) ... the mass killing sites where one portion of society conflicted with another. So instead of Robert et. al we have: club/sword/spear/bullet/bomb as the "natural" endpoint of a too-large / too-complex social entity. Lincolns America, Lenins Russia, Hitlers Germany and Maos China are prime recent examples of this behavior.