In answer to your questions:
1) ClassiPress has a featured ads slider, but if you're looking for additional options to featured ads these would need to be done via customization or you could look at some of the
AppThemes marketplace products, specifically child themes which include other features e.g.
Citrus night child theme which highlights featured ads and includes a ribbon.
2) Users are required to sign up in order to post listings and you can require it for use of the contact form, however there isn't a built in function for mail management
3) You can find examples of modified ClassiPress theme sites in the
AppThemes customer showcase, however we cannot cannot confirm who the developers were for these projects. AppThemes does not offer customization services, however we do have a
certified partners page where you can find developers for hire who are experienced at working with our themes.
4) As mentioned above, we don't offer this, but if you make contact directly with any of our certified partners with an outline of your requirements, they can provide a quote for the work.
5) The difference between the
standard and developer license is the the developer license includes the Photoshop .psd files. It really depends on whether or not your developer wants those files, but if you did purchase standard you can always upgrade later on. Thanks.