1. If this was something that became a popular feature request, then the development team would certainly consider it for a future release. We have a "feature requests" section of the forums for that purpose, so that members of the community can indicate their interest in any features not yet available ;)
2. Yes, this is something you can set from the ClassiPress admin dashboard.
3. Not at this stage, but would recommend you follow the
Appthemes blog as this is the first place where announcements are made.
4. There isn't actually any function to bill a customer after sale, so this would involve customization of the theme on your part.
:)