Website Registration, Invitation, Referral and Rewards System

We are looking to build a business membership community in Drupal 6 (may look at alternatives) that:- 1. Begins with importing LinkedIn profile of the registrant. 2. Membership is by invitation only (Pinterest style) where you have to be accepted by the community Administrator or introduced by another member of the community 3. Allows members to log-in via LinkedIn, Twitter, Facebook, Google+, Pinterest 4. Encourages members to invite others to become members, utilising their LinkedIn, Twitter, Facebook, Google+, Pinterest, Outlook, Outlook Express, Gmail and MacMail contacts 5. Creates a points system for each new member introduced by another that is still a member in 3 months (active user) All code is to remain in our ownership.