One page checkout

We have an existing website [login to view URL] that is fully operational. We like to add one page checkout to this site. Payment Gateway 1. Moneris Eselect Plus ([login to view URL]) 2. Paypal Right now customers have to create an account first and then proceed to checkout. We need to see the following in one page checkout. 1. Customer adds the product to the cart 2. Goto checkout 3. See their cart contents, enter coupon code if any available or given to them 4. After applying coupon they can proceed to checkout 5. Billing address, payment type, shipping all of it they can see on this page 6. If they want to create a password for future use, they can also do it on this screen 7. If they want to get it shipped to different address, they can do it on this screen. 8. We also add verified by visa on this screen . We are getting frequent cart abandoned with existing checkout method. I think we had purchased in a box from this site [login to view URL] that is not working. We like to get this done immediately. Thanks