stacking clouds needs muscles. Including finger tips ,tendon etc so I put this lazy script on.
I am assuming you got proxmox in a BOX any level 1 hypervisor ,can work on type 2 hypervisors but be prepared for dramatic panic error messages :D hyper-v is grand from a basic laptop with 4 GB of ram , vmware is read only so sad trumpets , Examples
Xenserver is fine and has awesome features for free ,like the full monty...including memory deduplication But it's lab only or tiny cloud. It's limited to 10 pieces of metal ,10 real life servers...following that you need to ...PAY? So that's not GPL violation but for suckers that don't get the masquarade. Again for lab it's grand or just get ten hugely extendible machines And by huge I mean ,bigger than what you possibly have in mind. Always bigger. and always extendible by at least 50% of initial size.
Xenserver is snappy and cool to use but proxmox = no limits so think big ,think no limitations.
Xenserver has some nasty old 4.x .Net Framework management gizmos that can be tricky to run on linux(use Genymotion for Android emulator tends to bridge gaps.I surprisingly seen large 4.7
I dedicated 8 gb for workstation ,24 GB to run a in a fedora 29 basic kit called "Boxes" Boxes is a ready to go live image packer that gets a vm ready only asking for a password.