Add a Function to My Site

I have a small request to be made for the Treasures Little flower shop web site. [login to view URL] I want to offer 5% discount to anyone who follows us in Facebook and a Further 5% if follow on Twittter. How I would like it is 1. When a person Follows us you record in the DB under the users account that they follow via FB and/ or Twitter. 2. A Pop up window comes up telling the customer they now receive either 5% or 10% discount off all sales for ever. 3. If they are not logged in but press follow prompt them to create an account so they they can receive the discounts. 4. When the place an order and proceed to Check Out ( the user account is checked to see if they have followed TLFS if so insert a line in the order called Facebook Follower Discount (5%) or Twitter Follower Discount (5%) or Joint Facebook Twitter Discount (10%) and to have a the discount shown as a -$ amount from the cost of the items ordered only, not off the Freight.