Hello from Ukraine!
Glad to see project like this. My team specialized on big projects like eCommerce and Portals.
We are concerned about the performance of the system is not less than the general appearance of the site. Our main tasks is to create a lightweight, fast, unique and recognizable by all, service.
We use all smart and new tools for build projects, like php, node.js, Erlang, html5, javascript (native), MemCached, PostgreSQL, Redis, REST API, SOAP, WebSocket.
We creating unique systems and it's providing to your project more safety and more speed.
Ready to discuss with you all the technical aspects and an overall map of the requirements and create SRS.