How is running a container in an LXC worse than in a VM? It’s not really, is it? No, not really. Kubernetes could also be built on top of the LXC as well, sure. There are a number of genuine benifits from running docker on top of an LXC, and it doesn’t compromise security or come with a significant performance drop (unlike VMs).
UNRAID is designed to run off a USB drive, they have recommendations on what USBs to buy on their site, might be worth a gander. You should be able to write all the info on your current USB to the new one without having to reconfigure anything.