Need fast fix in magento store -- 3

Need to make: 1. In magento store make one product for 1usd at top of the list and after purchase allow users to download it (if they dont pay allow them to download it too). But other product should work as it work, change should be made just to this one product. 2. Add facebook convertion tracking code. 3. Dont add more products to cart after login in checkout. For example, user add one product to cart, he login in checkout process and system automatically add products from his last session when he was logged in. I dont want this.