I will also add a cron job to check for new liked songs once a day after this big download of ~15,000 songs is finished.

So I actually made a python script yesterday that uses spotify's web api to make a list of urls of every song on every album that I've liked one or more songs on. I then wrote a shell script which takes the file with all the urls and fetches the songs as 320 kbps mp3 files with a tool called zotify using a burner premium account I made. Unfortunately, it can only download songs in real time and will probably take around a month to finish downloading all the songs so I just set it to run on my vps. The mp3 files are good quality and have proper tagging and album art. I think I may have done it.