community VS Mopidy MusicBox

The Kiss Linux repos are not outdated, just the "official" one, there is one that is actively maintained by the community. https://github.com/kiss-community/community.

Yes. The init scripts are written so as to be as init-agnostic as possible. See here to see what has specifically been tested. You'll need to either change what owns /sbin/init or, when configuring the kernel, change what executable it spawns as PID 1. Depending on what init you use, you may have to set up a service manager or gettys manually like this -- custom scripts are placed in /etc/rc.d with self-explanatory suffixes .boot, .pre.shutdown, or .post.shutdown.

back is packaged in the community repository: https://github.com/kiss-community/community

If you use the Official unofficial community repository, watch out for packages that might get dropped by maintainers.

Again, if you had bothered to read the sidebar you would have seen links to both the community site as well as the community github repo.

I am very exited for https://kisscommunity.org, the possibilities are endless!

Kiss linux is what you are searching for

This might not be exactly what you are looking for but KISS linux (https://k1sslinux.org) is a distribution that doesn't force ANY init on you, supports disk encryption ofc, it's probably the most light and minimal distribution out there (the core install has 7 packages), it's rolling release.

Is there a reason you need to use carplay instead of something like pi musicbox? What exactly is the USB dongle for?

I saw something here on reddit where people were taking the little $5 raspberry pi zero's and basically building their own chromecast audios with them. I am not sure this is the same thing I saw but I found this on google. https://www.pimusicbox.com/

I have a few rooms in my house which I have audio, but they are far enough apart that I won't be trying to stream to all at once. I am also a mostly Apple user, so I use Raspberry Pi's with Hifiberry AMP2 and shairport-sync (AirPlay target). I can select any of the Pi's as the speaker output on any Apple device. There's also a pre-made Raspberry Pi distribution called pi music box which also offers other protocols than AirPlay.

Get yourself a Raspberry Pi and battery pack if you're mobile, and check this guide out. That'll run Spotify 24x7.

Look what I've found: https://www.pimusicbox.com/ This should perfectly suit your needs..

Currently, my plan is to use https://www.pimusicbox.com/ with some sort of DAC, an undetermined raspberry pi model, and a micro SD card for storage (total flac library is just under 500 gigs). I'm not incredibly well versed in pi projects (have made a few successful retropie builds for friends) and am an amateur when it comes to coding and linux. Regardless, this project will be a hobby , so learning, failing, and growing are all part of the plan.

Pi MusicBox

https://www.pimusicbox.com/ I found this which has chromecast support and airplay, but it doesn't support rpi4 it seems