Thanks so much for all you input, I installed the ESXi free on a HP Server, yes, it is a lot simpler than I imagined.

So far all went ok, managed to installed a few test Guest OS.

OK, I know this is a free version so I am not expecting a free lunch, but is the following possible ?

1. GPU passthrough, not to run things like Autodesk Revit or Adobe Cloud Suite, but enough power to run decent graphics software such as Sketchup and other simple art software that will look for a GPU with 1GB minimum.  I read it required a vGPU such as a P100 or Tesla P40 etc that are supported by ESXi, anything not on their list is a no no ? 
because when I am eventually learned all the basics and tested enough, I have plans to implement the paid version for other places.

2. Is it safe enough to access VMs using RDP without commercial SSL/Cert ?

3. What would be the best way to restore a backup image (ie. Acronis) into a VM, I plan to test a small office by restoring one Server 2016 image into VM, and then the two wks into another two VMs.

Learned so much already just by reading replies, thanks so much.