That echo mini looks fun, but what I'd really like is a small touch-screen linux device that can both play my bandcamp local files and run Spotify, but that I can lock down to no other apps (no distractions!).

Should I just build one out of a raspberry-pi + screen, or are there better options?

Depends what you consider "better". There seems to be small Chinese devices that can be delivered with either Android or Linux. E.g. search for Pipo X8R (can't say it looks very good, though). They also seem to sell Windows mini PC's - maybe some of them will run Linux without too much trouble.

There are also a number of providers of displays marketed for RPi, some with mounts to attach it at the back. E.g. see EYOYO on AliExpress or elsewhere. Here's one[1].

This certainly makes the "build one" option quite trivial, since for most it's just a matter of screwing the RPi in and attaching a couple of cables. I'm planning something similar when I get time, and suspect I'll end up with one of those monitors.

[1] https://www.aliexpress.com/item/1005009871559093.html

Not exactly what you want... You can likely run Mopidy on a pi and lauch browser in kiosk mode to show its web interface. If you don't want display and ok controlling from your phone then you can run mpd for local files and librespot as spotify speaker.

I wonder if that Echo Mini can be hacked/reprogrammed for just that purpose.