It’s all open-source. Download what you need, installing it as you need.
I’m basically in a similiar business, all my clients use OpenSource for Servers.
I run NethServer native on Hardware, but mostly a client buy’s a server (Like HP MicroServer for a SME).
ProxMox is installed on the Hardware, and virtualized NethServer is installed in ProxMox.
Mostly a Synology NAS takes care of backups - and synches the data and images to the clients home for an offsite backup.
I use OPNsense hardware for the Firewall, but in one instance a NethServer without virtualization is doing firewall, Monitoring and all server services.
UPS are usually handled by a Raspberry, configured for that duty.
This stuff is rock stable!
The NethServer Community gladly accecpts donations!
-> And is a great source for help, suggestions and such.
My 2 cents