I've set up a multisite with drupal 8 alongside a drupal 7 but not multiple drupal 8 sites.
The existing drupal 7 documentation was enough to go off. Definitely would recommend trying it out on a demo site first.
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 ...