1. In previous versions of ClassiPress, yes, ads were located in the same place as blog posts, however since ClassiPress version 3.0.5 we have been making use of WordPress custom post types and taxonomies. Ads are now posted under "Ads" and blog posts are under "Posts". You can read more about this
here.
2. Yes, you can see all the ads in your
wp-admin under the "Ads" section as seen
here in the ClassiPress admin demo, including ad expiry information.
3. With some customization of the theme, you could potentially achieve such a thing, yes.
4. Yes, there is currently a reCaptcha option and you can configure this from the ClassiPress admin (
see the "Security" tab of the settings). There are plans in a future release to allow a double opt in process if you prefer to have the customer receive an email for signup.