Yes, your “root” seems to be the same as my own “public_html”.
For me, the first question would be that of whether to move your current installation into its own sub-folder. Doing that is not necessary, it would only be a matter of convenience- or neatness-of-arrangement:
root/cgi_bin
root/stats
root/add-on-1
root/add-on-2
root/wp-admin
root/wp-content
root/wp-includes
-or-
root/cgi_bin
root/stats
root/add-on-1
root/add-on-2
root/primary
–
root/primary/wp-admin
root/primary/wp-content
root/primary/wp-includes
With multiple domains to maintain, you will soon find yourself editing separate files with the same names for separate domains, and there is where having each in its own sub-folder can make a huge difference in helping to keep all of that straight!
Moving your primary to a sub-folder can be done within WordPress or by using .htaccess prior to it, and that second method is what I use. Simply copy (keeping the originals as backups for now) all WordPress-related files in “root” to your new “root/primary” folder, then place your edited version of this into “root” as your new .htaccess there and log in:
## from https://my.bluehost.com/cgi/help/347#redirect
# .htaccess main domain to subdirectory redirect
# Do not change this line.
RewriteEngine on
# Change example.com to be your main domain.
RewriteCond %{HTTP_HOST} ^(www.)?example.com$
# Change 'subdirectory' to be the directory you will use for your main domain.
RewriteCond %{REQUEST_URI} !^/subdirectory/
# Don't change the following two lines.
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# Change 'subdirectory' to be the directory you will use for your main domain.
RewriteRule ^(.*)$ /subdirectory/$1
# Change example.com to be your main domain again.
# Change 'subdirectory' to be the directory you will use for your main domain
# followed by / then the main file for your site, index.php, index.html, etc.
RewriteCond %{HTTP_HOST} ^(www.)?example.com$
#RewriteRule ^(/)?$ subdirectory/index.html [L]
## index.php for WordPress
RewriteRule ^(/)?$ subdirectory/index.php [L]
For your add-ons, simply copy the *content* of a freshly-unzipped /wordpress/ folder into each new root/add-on#/ folder, and then it looks like here is how you would assign an Add-On Domain to its destination installation:
https://www.ipage.com/support/tutorials/view_tutorial.bml?kbid=6104