You may wish to start out with a VPS Reseller plan so that you can test the market
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It depends on your current setup, are the systems that your are currently running even suited to host VMs?
It could be done if you can shift your domains around to free up a system. This free server could then be used to host VMs. You could even create a VM to move the domains back to and eventually convert all of your servers over.
Still I would have to agree, starting with new hardware built for the task would be ideal, though it is possible.