Navidrome and it’s smart playlists is incredible. I’ve heard of Gonic and Jellyfin as other options. I think you can share a music link with Navidrome but I’m not entirely sure, I haven’t looked at it in a long time.
I use Amperfy on IOS without issues
Yes and yes. I do actually use a bunch of stuff but a lot of it is for experimenting. I regularly use Jellyfin, Vaultwarden, PiHole, Nginx, among a few others but for experimenting, I recently set up a container will Mullvad vpn so I can use that vpn networking for my qbittorent container.
Sounds very similar to my setup. All I would recommend is SSH through keys (and disable root login) and don’t put everything into the Docker network bridge. If you have containers that need a database or other container(s), make a network for those.
Obviously keep up to date with new updates. There are many services that can automatically notify you for updates like Watchtower. You can also set it up automatically update the container but it’s not always recommended in case of breaking changes.