A few tips:
If I recall correctly, the category/subcategory permissions are completely independent. You have to set permissions for each separately.
For the public categories, consider using tags instead of subcategories. It makes it easier for users to figure out which category to use.
[quote=“codinghorror, post:2, topic:45223”]
Categories are like walls. Build 4 and you have a nice house; build 24 and you have a maze.[/quote]
One downside with tags–users can’t set a tag on mobile initially except by publishing topic/edit topic/set tag/save again. Moderators can do it as new posts are created. Just depends on how important tags are to your site.
Avoid mixing group and category terminology, so call your private area, e.g., “My Clubs” (not My Groups) and then set up sub-categories which use groups to grant access to the sub-categories. Groups are for people and categories are for topics.