Are USB external multiple disk cases reliable enough for RAID? I think they are. I've had similar setups in the past though not ZFS. I've done this with LVM.

Are USB external multiple disk cases reliable enough for RAID? I think they are. I've had similar setups in the past though not ZFS. I've done this with LVM. In my experience it may be a good idea to not put any part of the OS on that raid, set the mount option "noauto" and have a background script that checks the raid/volume health first and then mounts it in the event that any USB connections are loose or disconnected or late to power up. That way you can always get into the OS without anything hanging.