I run Proxmox VE and Proxmox Backup Server on two machines at the same time. I pull the main backups from the main machine, where all the Vdisks are to the second one. Until now it works like a charm. The third of site machine is in the making

No server is overkill If you want it can afford or and can deal with the Energy consumption

Don’t use rj45 use DAC and Fibre

I did 10Gig a few months ago and I live it.