I know this is for Elan, but I just wanted to chip in here a bit.
I personally put 24 hours of downloaded music of the playlist “fresh love”. Because this playlist uses advanced parameters to only serve highly rated tracks you haven’t listened to in a while, hence fresh. This gives a lot of rotation in the list without having to do anything.
Then enable the feature that PlexAmp updates the downloads every start, and disable download over cellular (this is the default settings) and PlexAmp will automatically keep the list filled with 24 hours fresh downloaded music when you open it on wifi.
So now, unless you listen 24 hours in one go, this playlist should always have new and fresh 24 hours music for you. This works for me.
Of course, this requires that you rate tracks on Plex.