What features

What the ezmlm module does is send a subscription request to one or more ezmlm mailing lists that the module has been configured for.

To send such a request directly from another module you could call the function _ezmlm_subscribe_process($subs, $mail) where $subs is an array containing one or more mailing list addresses and $mail is a string containing the user's email address.

How you get the registration process to send the request is another matter, the user_register_notify module could be modified to do the job. Alternately you could add a properly formatted string to the email initially sent to the new user inviting them to join. See http://ezmlm.org/ezman/index.html for details on how to format such a request.

I'm not familiar with the Insert Views module, but it's description does not suggest that it is capable of carrying out any action other than displaying some content according to some criteria embedded in a node.

The HTML Mail module will I think do the html formatting for you.

The advanced user module can handle mass mailouts apparently.

HTH