Scales
Grinder (ideally available from you, with suggested setting based on provided brew guide).
Filter cone (Melitta, Bartleet, Wilfa pourover, something that utilises papers that can be picked up in a supermarket...or a V60 01 preferably, but 02s can be picked up, with Japanese papers, at Ocado).
Filter papers.
Pourover kettle. (Melitta & Wilfa cones could be used with a regular kettle at a push).
Proven brew guide for 1 mug, that you can use as a diagnostic. (for 2 or 3 cups just repeat the 1 mug recipe). Same grind can be used for large French presses. Basically keep it modular?