1. Yes, administrators can add ads from the WordPress admin dashboard.
2. Payment methods by default are PayPal and bank transfer options, although we also have a plugin now available to include Google Checkout. You could potentially add your own payment gateway as other customers have done, however this is considered a customization, and as such, is not officially supported.
3. All support for our themes is carried out via the AppThemes forums. We do not officially support customizations or third party plugins, but help with configuration such as custom fields is part of standard support.
4. Yes, you can select price per category.
5. A theme purchase is a license to use our products.
6 & 7. If you want specific changes made that are not part of the default theme, then these are considered customizations, so are basically up to you to implement.