I actually moved from another music service (my old ISPs reskin of some music service) to Spotify and I was also worried about losing my stuff from the other platform. My new ISP recommended Soundiiz to transfer stuff. I was skeptical, but it worked! They have a paid service with things like automatic sync, which I didn’t need. That would’ve also gotten rid of some limits, but I couldn’t get payment to work so I used their free tier, which required splitting stuff into 200 item lists because of the free tier limitations, but I could transfer stuff little by little. Soundcloud is one of the services they cover.

That’s funny, I’m actually working on something similar to what you’re describing. Basically an app that grabs metadata from various music sites (spotify for now), and streams the music for free from youtube.

I found this open-source attempt a while ago (haven’t tried it), but it seems like the maintainer wants to do closed-source stuff now :(

I’m working on that feature as an enhancement to my app Bongo. Right now Bongo just makes sharing songs/albums easier across services. I still need to add more options.