Build a Social Networking Site

We need to build a social networking site that will have the following capabilities. 1. Login via FB / Twitter / Email 2. Create Topics 3. Members will be able to Follow Topics 4. Follow other members 5. Socially engage through FB post, twitter post, etc. 6. Comment on topics and the ability to share them on FB and twitter 7. Suggest Topics to other members 8. Vote up/down comments 9. PayPal gateway 10. Complete, easy to use admin management of the topics, topic categories, members and everything I am looking for an experienced developer to create a website with some of the functionalities as Quora dot com but different objective. Some functionalities will be similar to twitter. Technology and platform must be scale-able. Social networking and publishing features will be inbuilt. Please go through quora dot com in detail before you bid to understand the login to all other capabilities. Without going through quora dot com and understanding the capabilities you need not bid. Design service also required. Thanks