Ah, from the technical point of view, getting notifications for new content only works on a per-category basis(?)
I also noticed that the search at the top on the main view seems to only allow to filter by specifying one tag, or am I doing this wrong?
If this is the case, the tag-functionality in discourse is indeed quite basic. (I had hoped for something like in github, e.g. “get all labelled as ‘enhancement’ and ‘help wanted’” and the ability to make the filters stick, i.e. create a custom main view from that). So if this is the case, I take my suggestion back.