Hi,
I don't know why all your emails are in draft. Did you check if there emails are in draft or not in V5?
When migrating only the global statistics are migrated. Due to many technical diffeences detailed statistic will not be migrated.
If you have the Enterprise version you can setup an Automation that will subscribe users who are member of a specific Joomla user group to a list of your choice.
You can safely uninstall your V5.