X-cart shopping system modifications

We are looking for 3 modifications for our x-cart based ([login to view URL]) shopping cart system. Invoicing Within the administration menu, we would like to be able to create an order based on a customer’s email address. Once finished adding items and discounts, we need to then email the customer an invoice and a link to pay the invoice through the checkout system. Additionally, if a customer has already placed an order, we would like to be able to modify the order and send them an invoice with a checkout link. Payment Restrictions We would like to be able to restrict payment methods by shipping zones. Mainly, we would like to be able to offer all payment methods to domestic (US) orders and Paypal only to foreign orders. Currently we just cancel the foreign orders and then ask them to reorder using Paypal. This is kind of clunky and would prefer to just restrict up front. Shipping options We would like to be able to offer Free Shipping on some items but have to be able to restrict it by shipping zones. We often offer free domestic shipping on some items but the way x-cart is currently coded it ends up giving free shipping to all orders. We have found a clunky work around (but haven’t implemented) by setting the charge per pound for domestic to zero and international at another charge but that is not very efficient and is hard to maintain.