1) This is not currently a feature of ClassiPress, and at the moment although there is a "% of sellers ad price" payment option, this charges the ad poster during the initial ad posting process. So if you wanted to have it function as you describe, it would take some customization on your part.
2) As above, purchases are not made via ClassiPress, only the ad posting process.
3) & 4) This is not a feature of ClassiPress, no.
5) All of what you have mentioned would require customization of the theme. AppThemes does not carry out customization work, however we do have a
certified partners page where you can find developers for hire who should be able to price the work for you.