If you are a student, try Microsoft's Imagine site. Note that your university must be on their approved list and they will validate. But you can get full Standard or Datacenter editions of Windows Server 2016.
Isn't imagine just a limited time use. And is the insider a permanent license too?
Imagine is a student entitlement.
The Insider program is for as long as MS wants to support it, but absolutely NOT meant for a production environment.
And accepting of whatever updates MS wants to push to your system, even if it breaks something.
But you can run multiple VM's in a regular Windows OS. I do on my Win 10 Pro.
3, 4, 5 VMs simultaneously. Just need sufficient RAM.
As far as I recall, the Insider program does not have a time limit, but again, part of the agreement is that you're using this for testing and development and not in a production environment. If you need to use this with live data, you need to purchase Windows Server Licenses (or find another option).