Complex shipping ASP script help

I need help either scripting or telling eCart what I want to do with a bookshop -

*If customer orders 1 book, then shipping = databasecolumn.minShipping
If customer order >1 book, then shipping = if (totalweight < 500g) $5, if (totalweight >500g) $10 UNLESS CombinedMinShipping < $5,$10 respectively, then use combinedMinShipping

*If customer country is NOT Australia, then skip paypal process and redirect to InternationalCheckoutSuccess. It already captures the data, she plans to review the order details, and send an invoice manually through paypal, then manually update the database payment status.

Note the customer country is not known until the checkout page collects it, just before confirmation. Selection>Cart>Checkout>confirmation>(suspended payment)>confirmationsucess>manual invoice>manual database update

Its confusing and overly complicated I know, but the person I'm building it for has absolutely ruled out using the AusPost calculator or fixed rate shipping, as well as using stored customer log ins.