1. No, at this time there are no options to specify number of images per ad package. It is a popular
feature request though, so potentially something we may see in a future release of the theme.
2. Yes, ClassiPress requires an instance of WordPress to run, and actually uses WordPress functions as well at the additional ones built into the theme. You can use other plugins, however please note that there will be many plugins that are not necessarily compatible with ClassiPress or custom post types, and so we cannot guarantee they will work.