The short answer
Do not hire a Head of Growth first. Your first hire should be a builder who can ship an experiment end to end, because the initial growth model has to be created by the founding team and a senior leader parachuted in will either copy someone else's playbook or produce a strategy nobody adopts. Match that first hire to your actual bottleneck: if activation is the problem, hire someone product-shaped, and if acquisition is, hire a marketer who can code a landing page. By ten people you want the four growth areas covered (acquisition, activation, monetisation, retention) with a dedicated growth engineer and an analyst, because in PLG the analyst is not overhead, they are the whole feedback loop. Sequence the squads in the order your funnel is leaking, not in the order the org chart looks tidy.