Add some billing fields to a WooCommerce checkout

We have two custom post types created by the wp-types plugins. One stores commission payments received by a wordpress user the other stores withdrawals for the same user. The difference between the sum of all the payments and all the withdrawals is the users 'balance'. We use wp-types to show these payments, withdrawals and the computed balance. We do not store the actual balance in the database at the moment. We have a Woocommerce store on the site and we want the users to be able to pay for their online purchases using either the stored balance or a normal payment method such as PayPal or a combination of both. This choice will be made by selecting a checkbox on the checkout page. The checkout page will show their current balance and they will check the checkbox to say they want to use some or all of the balance. If the checkbox is selected and the user wants to use some or all of their stored balance then once the box is selected a new box with the amount they want to use appears and they can enter the amount. If the user chooses to use some or all of their stored balance then as well as the normal Woocommerce billing processes we also want to add a new withdrawal as a custom post with the correct fields so that the site is kept up to date with the remaining balance for the user. This custom post currently stores the order number with a link to the order itself and this functionality should be maintained. It is a custom field of the custom post. We need the code to be able to make sure that the user cannot use more of their stored balance than they actually have. I.e if their balance is $1600 they cannot use more than $1600 at the checkout from their balance but they could top up the remainder with PayPal or whatever other payment processors we have enabled in Woocommerce. Emails The standard woocommerce emails should also have the correct information on them for the user and the admin emails. I.e these must show the choices the user has made, the totals used from the balance and from the online processor. Admin Pages Admin pages will also need the information adding to the woocommerce order page for the order received so that the admin can see the methods of payment on the order. The Admin commission account withdrawals will need to show the order number and a link to the order for the admin to click. This is currently enabled as a custom field in the Custom post type. Compliant Code The code must be written using the correct Wordpress compliant codex and compliant with the WooCommerce codex as well. The code should use all the correct filters and hooks so that updates to Woocommerce or Wordpress should not normally interfere with the code. The code should written be as a plugin and should be commented appropriately so that future edits can be made by other coders if necessary.