Build a Website

I am looking to build a membership website with a multi-vendor shopping cart. This can be done in two phases. I would like to get the membership site up and running first. The membership site will be for MEMBERS to join, network, chat, view video, radio streams, view blog, download documents, our software, register and view webinars. These are some of the features that know for sure will be included. However, we want a cool site with fresh new features. We will also need widgets/apps created as needed. The site will also be for CONTRIBUTORS. Our Contributors will be able to login and post/upload whatever they do (blogs, documents, webinars, services, products, live chat with members, forum Q&A, or stream live). We are in the process of having our software program completed, which is what this member site is built around essentially. The second phase of the website is the multi-vendor storefront. This will allow our members to post their product, services to the public. Would like the option/feature to open posting for the Contributors too because this may eventually be open to any seller in the future. This will be a great oppty to do some really creatively cool stuff for the right freelancer(s). We can maintain the site ourselves for the most part, we need you to create the core project, cool widgets, apps, plugin. Considering wordpress+multi-vendor cart plug-in. Inform us on why you think this would be a good idea or if not, what you would recommend and why.