regarding your questions:
1. If you dont want users to register from the frontend, then you can remove the menu item for User Registration by going to Appearance -> Menus in your WordPress Admin. however, the application still has a provision of registering new members from the Genealogy view. For this you would need to modify the code as currently there is no setting for disabling this.
2. as advised previously, we have deliberately not placed the user "admin" in the network tree. So you cannot register new users using the admin login. You can however login as the FIRST USER that you created when you installed the plugin and register the users from there.
3. The genealogy view is currently set to display 5 levels of the tree at one time. you can however drill down to whatever level by clicking on the username of any member in the tree. If you want to change this setting you would need to modify the code.
Hope I have answered all your queries.
Sarah | wordpressmlm.com Support