It took a while to get here where my Mopidy solutions is right now, an I can finally relax and just enjoy.
From running Mopidy-Iris- mopidy-spotify- snapcastclient and server with a Rpi3b connected to an external HDD for music library
and there was always minor problems, slow connection to Raspberry Pi, time outs, lagging etc etc, but in all it worked OK.
A year ago maybe I was thinking to upgrade to RPI4 but from my point of view RPI4 were a bit pricy AND hard to get in Europe.
In same time period I had an homelab running on another RPI3B (nodered,deconz and pihole)
so I was thinking why not running everything at one machine, one machine to rule them all 
I searched the second hand market for a mini pc with decent specs, and found a Dell Optiplex3060 with 120gb ssd, intel i5 -6core cpu and 16gig in RAM for about 120EUR.
Installed Debian bullseye, Virt-manager and all its components
And know I running my homeautomation software at one Virtual machine, and Mopidy , Iris mopidy-spotify and snapcast-server on another Virtual machine and my music library is still on an externalhdd connected to the Mopidy-virtual machine , It works like a charm, my snapcast clients is RPI’s I have one rpi zero W , and two RPI3.
Greeetz!
