I do something very similar. I have all my music on a network share with a playlist folder inside. I run a script that copies all the lines from an .m3u playlist file and copies them to another music folder inside my user folder, converting any FLAC files along the way.

I then user SyncThing to synchronize that folder with my phone. Makes it super easy to get all my music and playlists when I upgrade to a new phone.

a = *lines from playlist file*
new = *destinationFolder*
# If the mp3 version of the flac is older than the flac or doesn't exist in the destination,
# convert it from Flac to variable bitrate mp3
  if [ "$a" -nt "${new[@]/%flac/mp3}" ]; then
    echo Converting $a
    ffmpeg -y -i "$a" -qscale:a 0 "${new[@]/%flac/mp3}"
  fi

There's some cleaning and other steps done but I'm willing to share or provide more details if anyone is interested.