How many virtual cores for VPS can be created on a certain configuration? How to correlate them with physical CPU and threads?

Question

Network administration

Hello community.
I'm going to rent a server to host a number of VPS on it. As mine, and friends and clients. On VPS-kah their sites will spin accordingly, and not only - maybe even the video will be encoded, then whoever wants to do what.
Question. How many virtual cores can I create with the following configurations:

• E5-1650V2 (6 cores, 12 threads)
  
• 2 pieces Intel Xeon E5620 (4 cores, 8 threads)
  

There is no question about RAM or disk space, there is guaranteed enough of it to distribute it in sufficient quantities without exceeding physical limits.
KVM virtualization.
I do not quite understand how to distribute these capacities between virtual servers so that there is no overselling. And I don’t understand how VPS hosters act in this case. Basically, they write - they say, so many Intel Xeon cores. And how these nuclei correlate with real ones is a mystery.
How can I do better?
Create virtual cores by number of threads (12 or 16) ?
Create virtual cores based on the number of real cores (6 or 8)?
To what extent can you create more virtual cores than real cores (or threads) so that the service remains of high quality? And is it possible to do this at all, or would it already be dishonest?
Thank you.

Answer 1

Without overselling, you need to create the number of cores by the number of cores, not threads. That is, four cores in the system, four cores for all vps

Answer 2

I do not quite understand how to distribute these capacities between virtual servers so that there is no overselling.

Why do you need virtual machines then?
Bet on real hardware.
;)
It only makes sense for your specific workloads. See, try, check. You never know what specific clients will be in your case.
If 99% of your hosted clients give a load of 1-2 visits once a week, then why do you consider overselling to be unfair?
Without overselling, hosting is not a profitable business.

Answer 3

Without overselling - it's not fair. And stupid.
98% of the time resources will be idle if you distribute them 1 to 1.
The vast majority of sites are not loaded.
If you want to do it honestly, then you just need to monitor the load - no one knows exactly how much the load of the virtual machine will give you. But you can find out.