Is it possible (and if so, how) to configure WordPress blog to support these feature for user comments? I want to use built-in comments, not 3rd party services like Disqus. If something cannot be achieved by configuring WordPress itself please suggest plugins that can achieve the following:
1 + 2) Every user that would like to leave a comment must be authenticated. Supported authentication methods must be Google, Twitter and Facebook auth, no other (e.g., it must be impossible to log in using generic OpenID provider or the built in WordPress authentication etc.)
3) If a visitor provides an email address, they can check a checkbox to be notified of new comments
4) Comments should be flat (not visually nested) but should allow references to other comments.
5) If there are too many comments, they should be loaded dynamically as user scrolls down (i.e., similarly how Twitter or Facebook work).
Can this be achieved using WordPress built-in comments plus some plugins?