TrueNAS

TrueNAS seems to do a lot of what I'm looking for in a NAS appliance.  Core is the FreeBSD-based version, which would have better networking.  However, Scale has better software support since it's Linux-based.

Installation of TrueNAS isn't too bad.  It's the setup that's a challenge!  Mainly, getting Windows to recognize the SMB setup has been an exercise in frustration.

Otherwise, one issue is the dead space on the "boot pool" (forum post)--while the pool can be expanded, not sure what to use it for.  Containers, perhaps?

The other thing is, perhaps for reliability I should mirror two 1TB drives (flash...) and have a partition on those drives as a separate vdev (forum post).  It's a bit overwhelming to understand how to set up a good configuration.

Also, Youtuber "Raid Owl" has some videos on setting up NAS appliances.