1. In the Classipress admin settings you can disable the "Prune Ads" option and with that the ads will remain though they would be marked as expired.
2-3. No option on this yet and by default the registered user role is a contributor. There might be a plugin that can do this.
5. There is no option on this yet and may require additional coding and or through the use of plugin to implement.
6. Not an option but there is a plugin to moderate user registration.
7. Implementation of certain feature is dependent upon the number of users requesting and voting for it.
8. Classipress already includes an advanced search filter of which you can check at the demo page.
For additional features, you may post a request on it at the ideas exchange page
http://ideas.appthemes.com/forums/84267-classipress.