Products review site

Hi there, I am looking to have a website designed which allows merchants to list their products with photo and text and then the general public to review the products based on their experience(rate out of five, comments etc). I also want to have a list of sellers by each product which could allow for affiliate links, advert spaces on each product page, page to be optimized for the search engines for the product name. I would also potentially like general public to advertise their used related item for sale on that page and we get a percentage of sales as a fee. So there will be one page per product with all the above features - almost like a searchable directory but with more information. The design part is not so important as i can do this - but what i need help with is the basic back coding and structure etc. Most importantly i would like this to almost run itself so everything is updated by the user with minimal imput from me. Many thanks!