BuddyPress.org

You’ll want to use Paul Gibbs’ Welcome Pack plugin for new users to have a bunch of default friends :
https://wordpress.org/extend/plugins/welcome-pack/

By default, Welcome Pack sends friend invites; to have the plugin auto-accept friend invitations, read this:
https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/standard-group-for-new-users#post-69096

For your other questions, please post them on the forum.