Customize a simple twitter clone script

I am planning to buy this script but I want to customize it. Link: [login to view URL] I want the following features added: - Users/Visitors can signup with facebook/Twitter details - Users can invite friends on facebook to join my site - Anything users post on my site, should automatically appear on their facebook/twitter page. - Implement a mail system where I can send emails to all users or selected users. Finally I have an old phpfox database, I want all the members transferred to this script (new website) The implementation should be bug free, all bugs have to be fixed, and you should be available and willing to fix any bug found later in the future. My budget is $30 - $100