Backup Spotify playlists with Time Machine

Ok, so I've searched through a few threads about Spotify backups here but didn't find the answer to my question.

Last year I discovered that my Time Machine seemed to make backups of my Offline playlists in Spotify.

This raises a few questions to me:

1) Is it possible to have TM make backups of Offline playlists, where it then would be possible to restore all playlists in the case of a failure due to a Spotify server issue or any other 'bug' causing my playlists to disappear?

2) If it is actually possible to do this, I guess you will have to have every playlist that you want to backup in Offline mode, otherwise I guess it won't be possible for TM to back it up? This would mean that when you reach 3333 songs on your computer you wouldn't be able to back up your entire Spotify library anymore (due to the current restriction from Spotify allowing a user to have a maximum of 3333 songs in Offline mode on a single device)?

3) I remember from last summer that my TM seemed to back up my playlists while I kept them all in Offline mode. However, the space needed to back up my 1500-2000 songs seemed to be approx. 25GB which sound a bit much since that means that a song would require 16.7mb of space based on (1500 songs, (25000mb/1500)).

Any input about this would be highly appreciated since there are so many forums covering this issue and so many different answers to what is true or not.

Some people clain that you can actually backup your Spotify library by simply 'drag and drop' the playlists into a text editor...?