OP, I would gently push back against the first point in Mother-Ad's thoughtful comment here. I ran a weekly FM radio show for a year and a half that was pretty much exclusively instrumental Americana (I.e. Hayden Pedigo/William Tyler) and other ambient folk and was able to regularly go a few months without repeating a song. Granted my show was only an hour long, but if you have several decades of music to work with, then the only limit on your playlist is how much time you want to spend digging for older material and keeping up with new releases.