Sure you can, I have seen many people do this, not sure how as I have never had a license but you can do it. What is your forum going to be based upon?
yes you can but when selling the forum make sure you let the person know the license is not included.
To change the address you can use you would log into the vb site and change the license profile which will allow you to install the system on the new URL.
this may be allowed, but I wouldn't do that
when I would buy your site I would like to get the whole site. I can not use vbulletin without a license, so I would also have to buy license for it after I buy your site