Help with Web Developer task

I'm investigating the prospect of starting up an 'online trade show' site for retailers and designers of high quality children's products and gift and homeware products. The concept would be a B2B membership only site where retailers can source products and brands/designers can showcase their collections24 hrs a day, 7 days a week. We are only in the initial stages of nutting out this concept but so far we would require the site to have the capacity for individual pages for each designer/brand, email marketing function, social integration - predominately Twitter, a variety of contact forms e.g application for membership retailer and designer, contact forms for each designer/brand etc. It is our plan to monetize the site by charging a monthly or annual fee for designers/brands to showcase their products. Membership for retailers will be free. We would also like a blog attached to the site where we can feature products and the space for banner advertising. I really hope this makes sense to you!!