Providing VPS from dedicated servers?

[Franburgs]

Hey, as the title suggests I am looking to provide VPS for my customers. I wanted to ask a few questions. I have read a lot of articles and everyone seems to give a different opinion, can I virtualize the threads of a CPU or is it just the cores? What is the best dedicated servers specs (CPU, RAM etc) to be able to cost efficiently provide around 20-30 VPS for 4x8 VPS and 6x12 VPS? I do not need anything crazy as users will be running non-critical programs. I do not want customers to use other providers as I will need the vps in the same server rack as my main servers. Any reviews on GTHost.com or Hostpresto.com dedicated servers? What host is better? Why?
I will be purchasing these dedicated servers and then splitting into VPS using KVM, Porxmox etc. Any tips in managing or what is the best way to go about this would be great.