New website - database rich, seo not too important

I am attaching a sketch of the home page which will explain this better than words. Bit like ebay but free to users. No post, so local buying and selling. I have the domain name. The better the website, the more users to be expected. Minimum 5000, I'd have thought, all of whom will require to log in to this website and upload a photo and description of what they have for sale.