I have a stash of both fabric and machines. Am in the process of rehoming some of the machines. Stash - I currently have no plans for downsizing yet. I do donate some fabric here and there as people ask. I am making some quilts this year that will mostly come from my stash, including piecing the backings but DH has no objections to its size or the space it takes up so the stash is staying. We are in the process of cleaning up and refurbing some of the machines because they do take up an enormous amount of space but we are mostly giving them to people in need. Not sure what to do with some of them.
All this being said that I think your guidelines might work for some but not everyone. It has however started a great thread.