1. Sorry, I don't know what you mean. If you're saying you wish to auto-subscribe members, then this is possible from the Mailing List Manager. You simply tick the boxes for the usergroups you wish to automatically be subscribed - ensure to include your default registered users group (the group they land in when they first register) and any other groups you may want automatically subscribed.
2. Unfortunately not, it wouldn't serve much purpose though - the sidebar system is for external mailing lists only (emails not belonging to registered users). It's currently the only way for users to sign up to an external mailing lists without you manually adding them in the AdminCP.