HexOS is built on TrueNAS and looks promising as a simplified version. Looks like it isn't available yet but I think you're who the kind of user they are building it for.
Don't know anything recent, but years ago they began blocking network traffic between rows. That killed what little self hosted LAN play was still happening but kept stuff from spreading across the whole BYOC.
Yes, but it is also set up as an OS image.
I think there is a process for persistence, but without some effort, changes are lost for OS updates.