Do I interpret this right:
The "hierarcy" you refer to is manifested as tags, i.e you're not talking about an actual aggregation or some applied widget, right?
When you say the reader should be able to "follow the text both ways", you mean access to a parent tag and children tags. The parent tags are the tag pills. Getting the children links to show is definitely doable, and should even be very easy - but unfortunately I'm a bit sucky at this so I'm not sure of the commands. Tobias has a
tagglytagging plugin for tw5 that you may want to try. (For some reason it is not performing correctly for me.)
And to "include a tiddler inside another tiddler" - sure, you just transclude, i.e type {{TitleOfTiddlerToSee}} in the other tiddler.
<:-)