Custom Social Site

I would like to customize open source social site (I have elgg in mind) and add additional modules, I. E. 1. Ability to manage catalog of entries and meta data about each entry 2. Ability to search the catalog by the meta data 3. Ability to copy catalog item from other sites to this catalog and add meta data 4. Ability to "assign" entries to members 5. Ability to share entries assigned to self to contacts 6. Integration with all major social sites to view/connect with contacts in all of those 7. Ability to rate entries 8. Search by meta data shall provide an ability to rate meta data accuracy 9. Ability to auto modify meta data for an entry based on business rules 10. Administrator super user shall be able to setup business rules for auto update meta data using UI I also want the site to be designed following agreed upon look and feel requirements, no Flash shall be used I would like the site to work on all browsers including major PC browsers, Mac, and mobile