SSW Additional Checks plugin allows super admins to perform additional checks before allowing registered users to create sites using Site Setup Wizard. You can make use of a filter ssw_additional_checks which is added to Site Setup Wizard and perform your own checks based on your own conditions.
Requires a wordpress multisite subdirectory install and Site Setup Wizard installed.
As an example this plugin has a check to limit users from being able to create only 1 site using Site Setup Wizard. You can modify the number as per your requirements or create your own function to perform additional checks.