Setting up a word press multisite on an existing server with multiple sites

I have a main domain with several add-on domains and subdomains installed. Many of the add on or subdomains have their own wordpress install. No problems except I am constantly chasing updates. I want to create a wp multisite and install all new instances in a subdirectory model using the multisite. I am not worried about migrating the existing sites yet – just setting up the new one. Question is can I go forward with my existing server and install the multisite in an add-on domain making it the root for the multisite or does it need to be in public_html directory. Do I need a fresh server install?