best way to cluster and migrate containers

Hi All.

I'm hoping for everyone's views and everyone's opinions on this

I currently have 5 proxmox servers all running separately (not in cluster) and I want to start managing them all from 1 panel and do migrations, backups, etc...

currently I have an old NAS box which I use for NFS storage which contains ISO's, Backups, Templates, etc...

they machines all currently backup fine every night via NFS to the NAS box... (takes few hours but works fine)

I want to be able to manage the servers via the Single panel, do migrations with almost zero downtime (dont mind a min or 2 downtime because the upgrades, etc, would all be done over night, e.g. 2am)

the only thing i can think is at the moment all the servers have containers and VMs running on them!

however clever me made sure the IDs of each container/VM was never used on another machine so there all unique! ;)

what would be the best way of me doing this ???

(NOTE i have 1 spare server doing nothing so i can put it into standalone mode to move the containers all off the servers if i need to start them afresh)

Regards

Simon