I am trying to implement an action that allows a user to manually send an email notification to other users informing them of changes/events related to a document. That is, I would like to allow the users of the system to locate a document, click on the More Actions menu associated with the document and have the option to Send Notification. If the user selects this action, they will be presented with a page that allows them to select the target users, select an email template, edit the body of the email, and send the email (i.e., something similar to the action Email Space Users but associated with a document instead of with a space).
It sounds like you need to add a new dialog to the system, which will be launched via a custom action (that you've already done). Have a look at this wiki page for a starting point: http://wiki.alfresco.com/wiki/Adding_a_Custom_Dialog
