I would recommend an old/used ThinkPad W520 or better for this. I've been doing this myself since 2013. Put in a second SSD, max the RAM to 32 and this thing flies. Costs will be about $400-700. With the nv optimus card you can even play around with gpu passthru.
Please don´t. CentOS is based on RHEL and this platform so crippled, you can´t even live migrate with the new v7: https://bugs.centos.org/view.php?id=8281
In case you still read this - there is a very good alternative to Proxmox & own scripts out there - so you won´t need a cumberstone windows client/admin VM or a full cloud setup: webvirtmgr.
You can even choose your favorite KVM distro and install that gui on top...