Organizational structure is challenging. Public companies struggle with it as much as startups do. When I was at Google, I was charged with calculating PM/Engineer ratios by team as part of the research into our company structure. When startups ask me when they should hire a PM or what the span of control should be for a sales team, I share this experience.
In start-ups that are not tech companies, most of this advice still applies. Substitute "operations" for "engineering" and think of "product" as either a good or a service and you have an idea of best practice. We love the recommendation to keep the structure flat in order to foster collaboration. In reference to Metcalfe's law and its application to structure, keep in mind that the strength is in connectivity. Structure is but a part of culture that fosters connectivity. In short, think about the impact your structure has on nurturing collaboration and creativity in order to have greater potential for success!