> We hit production with a 3-person team in less than a year; and subsequently scaled the team to 30+ engineers spanning multiple sub-teams
Starting with a small skilled team to build the core and actively plan for a larger team at some point is absolutely critical for project success in my experience, especially with complex projects like this. That small team can have a much tighter communication loop and all keep a single unified picture of what the end goal is. When the team grows this single unified picture is no longer feasible so it has to be broken down into sections, which is a good thing, but if the core isn't setup so that the sections are sufficiently decoupled things fall apart quickly.