I’m going against every one of your requirements by suggesting a pixel 6 or onwards used on eBay and install graphene os, it has the least amount of bullshit and is stupidly easy to install even for someone who’s never heard of a custom ROM
What kind of applications would you self host on an android phone though? I have a few old handsets and I’m struggling to think of services that I would want to run on one
I’m in a very similar situation, too many windows services running in the background. Casaos is supposed to be a user friendly way to set up a bunch of docker containers on linux for Plex and the arrs amongst other things. I can’t speak for how easy it is as it’s something I’m going to be exploring in the coming weeks.
I’m really getting the push I need to finally get rid of the last couple Google services I still use