User blog comment:Adnoam/Restructuring Qualities and their categories/@comment-25219384-20180314221114

Update: I've made step #1 in my list above easier:

Go to any page in Category:Qualities without Category. You'll see a link to create the missing category, including the code to put into it.

When you go back to the quality page (you might need to force a refresh from the Edit drop-down menu), it will either show the collapsed list of categorized pages, or (if the category is empty) tell that no pages use this quality.