You will not need to worry about transferring the values to the confirm or the checkout success page because the values are stored in the cart. So long as you don't clear the cart you will have the values available for your store order summary and store order details server behaviors. You may need to update the cart display that is on your confirm page to include this new column or at least the value from the column.
For the problem you are having with the radio group you must ensure that the names of the two radio options are the same but the id is different. This is the key to getting a radio group as opposed to two individual radio buttons. If you can post back with your cart display page that has the code for the radio buttons added to it I will take a look to see if I can spot the problems.
