Lubuntu
My first foray into unix-likes was oprnbsd with fluxbox. I eventually moved to openbox. Lubuntu with lxqt gives a nice simple openbox experience with a menu and stuff. I customize it to have openbox present the mouse menu instead of the whole pcmanfm desktop thing.
I’ve been using Linux for a couple decades now – I use Windows at work and came to like bing desktop; it’s unexpectedly nice.
It could be a music server with mpd – then you could configure it to stream over http to other devices. Or you could configure it as a client for a music server you keep somewhere else.
Thunderbird, and probably betterbird, is too bloated for my taste.