I keep eyeing OMV but haven't splurged on running a NAS with multiply-redundant drives separate from my application server; currently it's just an RPi4 as a docker host, with rsync keeping two USB drives in sync with each other.
For instance trying with an old low profile PC, wake on lan didn’t work half of the time so I gave up, and just let the drives sleep. But they would also fail to wake up sometimes.
All in all a NAS is not that expensive (I have one I bought for 400 or so, and it’s lasting for 15 years now…), so it’s hard to justify the endless tweaking of a solution that could work the same if done well.
BTW even with a commercial NAS , ssh access is configurable, major scripting languages are there, and recent ones have docker I think. For the really custom stuff, like you I use Raspberry Pis that mount the NAS files as needed.
As you said, it's very low energy and zero noise (rubber feet and quiet fan).
It's also effortless to set up and run with their RAID system and syncing etc is very good. It'll let me know if there is a problem with a drive, it keeps itself updated and I've never had to reboot it.
I do not use it for Plex as it wouldn't be able to handle it. They are a bit under powered but they're very optimised for their main purpose, Network Attached Storage, and that's the most important thing for me.
It is also very neat and tidy, unlike most home made solutions.