Hi
Where you put the Playback Channel Strips all depends on how you want to work. The basic concept is that at Patch level they will only work in that particular Patch. At Set level they will work throughout that set (with or without additional patches in the same set). At Concert level they are Global.
You may find it useful to make one Set or Patch with the right number of Playback channels, map the Screen controls, then make copies of the Set/Patch and simply swap out the Playback audio files. That way you only have to do the Control mapping once.
You could also save the Set/Patch, for future use.
HTH
CCT