This is what I have set up so far and it seems to work for us.
Right now our forum is private, we replaced our technical distribution list with Discourse. I have a category with a sub-category by product/feature. I have additional sub-categories for our competitive and tools discussions. These are all private categories restricted to employees. I will have an almost identical set on the public side when that opens up.
The choice of sub-forums was done so that SMEs could watch just their sub-categories if that’s what they wanted to do. For product owners, I required them to subscribe to their sub-categories. For our field they typically use mailing list mode so they see all the sub-categories.
I was originally confused about how mailing list mode worked as well, hence my feature request which turned out to be a misunderstanding.
Some of your requests I’m not sure about, but if you were to join my community as a user today it’s totally empty, employees see their forums, and admins of course see it all.
When I turn on the public side the public will only see the public categories and sub-categories.
Not sure about hiding users, but the rest is working for us.
thanks
-awl