Forgive me if this has been asked before, but is there anyway to add an entire folder of music to a collection? Or define a folder (with music) as a collection?
This is not possible.
Not impossible but not within the webui and not without some work.
Pending the merge of a PR to the python-plexapi library, you could create a simple python script to achieve this. Here is an example. I actually needed to do this for an arching series of AudioBooks. Worked out great. Although my solution may not work perfectly for you.