The custom form builder allows you to include additional fields to the listing form which is specific to the category to which is is applied to. You can see from the
Vantage admin demo what kind of fields can be added, and please note that the default fields relating to the contact information, address/map and images are there and not editable from within this form. So in terms of your question, a business can add images and information to their listing, even without a custom form.
You can charge for placing the listing, and allow editing, but the edit itself is not chargeable by default. The
AppThemes coupons plugin will allow you to create coupons for our themes. If you wished to share the user data between theme installations, you may wish to consider a
WordPress multisite setup. Thanks.