Custom Magento checkout

I need a few alterations in my Magento checkout process 1. Make checkout simple by only asking for client's email and comment. 2. Change total calculation by including the order number to the 7th and 8th decimals (Grand Total = Total + Order Number. Example: If the total of the order is 35.84BTC and order number is 53 then the Grand Total will be 35.64000053 BTC Notes: My Magento store calculates totals in BTC (Bitcoins) which is a virtual currency. All other payment methods are disabled. You will have to change the Payment Information checkout step to display a payment address and the Grand Total. Please contact for visual representation of what I need.