Need Advice Picking A Media Streaming Package

I still consider myself "new" to this self-hosted business, even though I've been doing it slowly over years. I have a Pi 4 with a few things going on (SMB, Node-RED, VPN), I have a miniPC running HomeAssistant, and I recently acquired a Dell Precision 5820. I installed Proxmox on the miniPC and the Dell, and now I want to self-host my music. I want to use the Dell for this rather than the Pi, as the Pi is doing its own thing and I don't want to mess with it.

In my research I've opened dozens of tabs and come across moode, mStream, snapcast, volumio, Plex, and so many more names. I'm a bit lost, and reading through wordy descriptions is only confusing me further.

At the most basic, all I really need is something to stream music over my network. Ideally the music will be locally hosted, but I'd like the option to use internet sources as well. I have a few gigs of MP3s and (don't laugh) WMAs from *many moons* ago. The Dell has a 2TB HDD and I plan to add more, but that should be plenty for just music. I don't really have any need for serving video at the moment, I live alone so the music is just for me and my cats.

Right now what I'm doing is using an old android phone, streaming the Lofi channel from Youtube, connected to a bluetooth speaker. This plays 24/7 in my house. I've removed the battery from the phone and powered it directly so it'll stay on basically indefinitely. It's plugged into the UPS that keeps all the other stuff on, so technically it's got a much bigger battery now.

I realized I don't need to be able to play over bluetooth directly from the server. If I can stream to a network endpoint, I can just play that from the same phone connected to the same speaker. I can also stream this to a chromecast, if the stream supports the extra metadata like album art and title that would be neat. I could also eschew the phone and bluetooth entirely and build a little ESP32-based network streamer and plug directly into the speaker.

For the most part, the janky setup I use now "works." It works as long as my power isn't out (UPS keeps everything on for 15 minutes, turning off my main PC + monitors gets me 2 hours). The speaker has its own custom battery backup (its open source) that will keep it on for at least that long. It works as long as I have internet, which does go out occasionally. If I lose internet for a while, I *can* use my work phone as a hotspot, but that sucks in general.

The way I listen to music typically is in the background. I don't want to pick a song, or go through a list, or even ask it to start playing. In my mind, it shouldn't ever *not* be playing. It's quiet, volume is 2/15 on the old android. I have a speaker in the bathroom, I use another phone to play either Lofi or my YT Music auto-playlist when I take a shower. Not super convenient, it would be cool to have another ESP32 streaming from the same endpoint as what's playing from the other speaker. Have it turn on from Home Assistant when I'm in the bathroom and the humidity starts to rise, or something silly like that.

Sorry for the ADD post, I just typed stuff as it occurred to me. I'm sure there's a simple solution for what I'm trying to do, I just got lost in the details and all the options and overhead that I just don't need. I would love any advice or direction.