Lenovo m900 tiny
They're small, cheapish, and low power.
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.
Lenovo m900 tiny
They're small, cheapish, and low power.
This right here. The exact models I used when setting up a 3 node PVE cluster. Ram is expandable, multiple storage slots, good IO, and best of all they are CHEAP.
Whatever you have lying around. Keep everything in VMs and then it is easy to backup and migrate to new hardware at a later date. Good luck!