One last other suggestion -- maybe add a "Summary page" that displays the campaign send details, before the user submits the campaign? So instead of tab 4 having 'Submit' button, it would have 'Continue' and would take user to summary page showing send details like campaign label, the lists it is being sent to and the # of active contacts in each list; when it is being sent (now or scheduled), etc., and then it gives the user a chance to review everything to make sure it's correct before they hit "Submit" to go and schedule the campaign.
Some other email marketing software I've used prior has this capability--adding a screenshot for reference of kind of thing I am suggesting.
Thanks again!!