OP, If you dont have a proxmox vm template ready to go, here is a great starting place using cloudinit:
https://github.com/UntouchedWagons/Ubuntu-CloudInit-Docs
You can use this with the proxmox gui cloudinit config as well to add your ssh key to each vm/etc.
Depends on what you’re doing a bit. Databases? Hypervisors? Just files? If all of the above, its best to use an actual product this. Either foss like borgbackup or Urbackup, or something like Veeam which is a popular pay option.
If its a proxmox hypervisor, they have their own free backup appliance, but you need a second physical server to run it on.
If it’s just databases, most have a built in way to take a backup. Just google the name and backup. Make sure it’s running automatically and is moved to a separate server on each run.
For files, rsync is a great option.
Backup is step one, or even step 0, of setting up a server. The amount of frustration and even job loss a backup can prevent is always worth the expense of time/money.
Backup can be setup scripts/config files/automation if the data doesnt matter, but you do need it. Also, even if they say the data doesn’t matter, the data almost always matters. It may not now, but it will in 3 years when people use the server for real work and everyone just doesnt even begin to think about a backup until the server fails one day and they lose years worth of their grant and thesis data.
Backups can be simple, they can be complex. They can be free or pay, they can have gui or just be scripts. Settle on one that you can make work, and CHECK THEM OCCASIONALLY with test restores of at least a few files. If you dont test and find a working backup, you have hope, not resiliency.
Heres the link.