Build a classified webpage

We are developing a classified page, we have already the page we just need some features [login to view URL] 1. Customers can post free ADS, or pay for a featured ad(depending the package paid on PayPal the can get the picture shown different places) 2. as a visitor can browser the entire page searching for second-hand items of interest and take contact to our customer by login and leaving a message. visitors can only use our page to contact our customer and they will have to arrange the transaction themselves via chat or mail. What we are looking for is a person with the knowledge to create the right backend of the page we need a Person who understand about categories, the sub and subsub categories to arrange the page in a way that is easy and simple, we would need custom fields for the different subsub categories depending if its car, garden, cloth etc. This require that when our customer creates an AD, they will have to choose the path where to put the AD meaning where/which main-category, sub-categoires and subsub-categories the ad have to be places, example: (” vehicles”> “dealer” or “private” > “Toyota”, “Volvo”, “Hyundai” etc. ) As the customer choose the path for the ad to be placed, the options of free or paid featured ad will shown, as he will be translated to the paypal to pay and back to finish the ad. We need to have meta data and taxonomies filter for people to arrange the products depending what they are searching for Then we need to have banners on the sides, top and middle of page. The banners are different depending which category page we visit, car= car banners, garden=garden banners etc.(we upload the different banners. Only main categories decide the banners for the sub, and subsub categories with possibility of internal rotation)