A lot of that stack looks similar to mine, though I’m running bigger hardware for various reasons. You might want to go with something with more cores than an i5 depending on how much you find yourself utilizing.
Have you considered Nextcloud for documents and syncing functionality? I went through a few ways of running it before ended up with the Snap package which has been fairly solid for over a year now (Docker was good for setup, but upgrading was problematic if not kept up with religiously)
Vaultwarden is Excellent.
Calibre-Web is good, especially if paired with the application to “extract” books, and an app like Moon+ on mobiles
Audiobookshelf is pretty solid. Pairs well with Libation.
HASS I initially ran on my server in a container but moved to dedicated hardware so updating and reboots didn’t break automatons. Got a HASS Yellow for the PoE and Zigbee.
If you’re looking for audio/video library management, JellyFin is pretty easy to get running and has apps for phones plus many TVs. Finamp is a good mobile app for the music part
I run backups to a USB drive which is way to grab in the event of an emergency. Just make sure you test them every more and again, and possibly only connect it when needed if you’re at all worried about malware (a cryptolocker will happily take out any attached storage if your machine is infected).