1) You can set it so that ads are not published until payment has been made, which effectively means that people cannot contact them.
2) There is not currently an option for multiple ad purchases at the same time, although this is planned for a future release of ClassiPress. At this time, customers have to pay for each ad as it is posted, or not, if you have made ads free.
3) There is no built in internal messaging system.
4) I'm not familiar with GoldCart, but in terms of the search display, what you see on the
demo is how it works out of the box. Any change to this would involve customization on your part.
AppThemes does not provide customization services, however you can find developers for hire on our
Certified Partners Page.