In answer to your questions:
1. It would be possible on the homepage through
customization on your part, however by default, these custom fields would only be available to search in the category view sidebar as seen on the
ClassiPress demo site. For the ad posting form you can create a custom form with the relevant fields available, and if using cars as the main category, you can set the make/model as subcategories to select from.
2. The default URL structure is like this: yourdomain.com/ads/ad-name but you can also change the base structure from within the
advanced settings tab of the ClassiPress admin dashboard.
3. If a free ad is published immediately there will be a success screen to do this, if it's a paid ad they will see this plus receive an email.
4. This is not part of the ad posting process by default, however users are required to register before they can post and therefore you can collect this data at that time using a specific plugin
here.
Thanks.