Can I use this to backup whole PCs ? If so, would it be a good idea to run this inside proxmox VE as a PC backup solution?
Well, depends on what your client OS is I guess. There's a cli tool called proxmox-backup-client which allows you to back up OS level, I use this to back up the host OS of my PVE server.
I am not sure if this tool is available for Windows/Mac though.
I have 2 PVE servers and on one I have installed PBS in parallel, which works fine. Just a different port to get to the UI: PVE: https://pve2:8006 PBS: https://pve2:8007
Proxmox VE is a complete, open-source server management platform for enterprise virtualization. It tightly integrates the KVM hypervisor and Linux Containers (LXC), software-defined storage and networking functionality, on a single platform. With the integrated web-based user interface you can manage VMs and containers, high availability for clusters, or the integrated disaster recovery tools with ease.