It is possible to have a single civicrm wired to several CMS instances.
There is some documentation here
There are hurdles to get over, for example, how to synch users across the various CMS
There are other approaches to pull in data from other sites without wiring CiviCRM in to it including
For the multisite integration across websites to work, yes you do need to do what is outlined here. That with some a few enhancement that https://wordpress.org/plugins/civicrm-admin-utilities/, which Christian noted above, allows you to connect multiple websites on a WordPress multisite to the same CiviCRM instance.
Deleting a site in WP triggers deleting sites/nn/uploads folder contents. Unfortunately, that site still had a civicrm symlink pointing to /uploads/civicrm which the delete trigger followed and subsequently deleted.
Don't use symlinks. I removed without issue. Instead you can define resource paths in civicrm.settings.php file. Will take a look at updating ...