Regardless of how you manage your AOFs and higher level horizons of focus, these are ultimately just checklists you review periodically to for ideas about projects or actions you might need to undertake.

I have two mindmaps for my areas of focus - one for work and one for home. Within the mindmaps I have 7 areas for work and 12 areas for home. This may sound like too many, but I find that my focus shifts around naturally and having all the areas on the map helps me to keep them aligned. I'm ok with some of them having no projects and others having quite a few. I review them once a month and this works well for me.