Great post @paula! Yes, a process is needed. I have used similar approaches in companies I worked for, though not in grassroots communities where I expect it will be harder to rigorously stick to it.
I feel that we should roughly follow such or a similar approach, but also should take into account that at this early outset everyone is brainstorming and we want to listen to all voices, get the best ideas. So that means sorta that while we go down the pyramid to more concrete levels, we can all place our “sticky notes” to whatever level it belongs to, and that stuff we consider later on, once we get there, to elaborate and decide if / how they fit.
Note that this forum and matrix too are poorly suited to brainstorming. Maybe we can create a Mural (or use similar tool), that is divided into sections like above pyramid, and we can all draw our sticky notes to them. Then once we feel that we are sufficiently done with that we can organize a vidcall workshop to shift and filter, and refine?