I guess, they want to tell you, These nodes can be Cluster nodes,
while the message clearly said "Standalone Nodes, No cluster defined"
Its more like a feature than "bug"
That reply is out of context. you are not following the guide line provided by Proxmox team. what do you want? a solution or just arguments?
Test another VM with a proper guideline.
You didn't post much information for developers to understand.
My guess, If you have created the Cluster, its not working well, which is causing the reboot.
Extending the root partition is depending on your requirement, if you need space at root partition, since its LVM based you can follow any guide to extend the LVM.
This configuration will give you and three little kids headache time to time,
Why not Xbox 1X console just for games? it has multiplayer capabilities. and keep the raspberry pi for education purpose.