How can I submit a list of flagged nodes to the admin user?
I actually think you are trying to make this too complicated based on your feedback. The simplest way in my mind would be to have a view (using current userid as a contextual filter) that displays the items the user has flagged. This opens up a lot of nice possibilities such as being able to remove flags before submitting, sort, filter, table view etc etc. Then quite simply have a button in the view header/footer that "submits/emails" the view url and user id to the admin. The admin can have the same view just with an extra box for userid (or exposed filter or whatever you want).