How do I add a confirmation form after the user clicks on "Save" in an edit form?
In brief, this is what I think you need to do in a custom module:


After validation, override the submit function on the node form to submit to a new interstitial page (you'll need to implement hook_menu to create the new page)
Pass the node object to the new interstitial page and define whatever logic you need in the interstitial page's callback function.
Create a new form on the interstitial page that runs node_save on submit with node object that was passed to it.