Best practice using activation key

What is the best way to build a new site on an existing site and how do I use the activation key in that process? I have an existing Wordpress site that I want to replace with a completely new Wordpress site with the Intuitive Pro theme. I was thinking of building the site in folder of the existing site. (domainname.be/new) And when the site is ready to publish I want to migrate it to the main folder of the domain. Is it possible to activate the template in 2 Wordpress instances on the same domain? Or is there an other workaround to do the migration?