The first ten hires are the room. The next ten are the room someone else builds. The job between is to make sure the second room is the same one — and the only honest way to do that is to be in every loop yourself.
Calibration is the discipline
Three calibration cycles over eighteen months. Each cycle pinned the bar to specific writeups from the last cycle, not to a memo. The writeups did two things: they kept the bar legible to a new interviewer, and they made the bar revisable as the work changed.
Growth seams
A team going from three to thirty crosses three seams that all happen between N=10 and N=18: the seam where the lead can't review every change, the seam where the lead can't read every doc, and the seam where the lead can't be in every interview. Each seam needs an explicit answer before the headcount crosses it — not after.
What I'd do differently
Less optimism about "we'll figure out reviews when we get there." More written-down rules about which decisions the lead retains and which decisions move down. The rules can change. The absence of rules cannot.