Is there a way to send password to the user through 'Welcome (awaiting approval)' email?
Dig into these modules and you'll find something worth (quotes included are from their project pages):


Subscriptions:


  ...enables users to subscribe to be notified of changes to nodes or taxonomies, such as new comments in specific forums, or additions to some category of blog. Once enabled, all nodes will have an additional link that allows the user to change their subscriptions. Users have tab on their user screen to manage their own subscriptions. Users can also set an auto-subscribe function which notifies the user if anyone comments on posts they have made. Admins can turn this on by default.

Notifications:


  ... This is a complete Subscriptions/Notifications Framework aiming at extendability and scalability. It allows any number of plug-ins defining new event types or subscription types or a different user interface.