OpenCart checkout questions

I am now looking into updating the GoogleCheckout payment module, to make it more compliant with Google's Terms & Conditions. My plan is to make it an express checkout, without having the customer to log into OpenCart. The customer will only to log into his Google account when he is on the GoogleCheckout payment gateway page.

I'd like to pass all the individual products and OpenCart's tax rules to Google. The shipment quote will be implemented as a callback function, that is, Google calls back OpenCart to get a quote, at which state OpenCart knows the shipping address and can invoke the appripriate shipping module. So this is my plan.

My first questions (there are more to come):

1) The product discounts: Are they inclusive sales taxes? If so, if the store is set to 'Display Prices with Tax:Yes', do the displayed discounts alredy include the sales tax, too? And if the store is set to 'Display Prices with Tax:No', are discounts displayed without the taxes, with the taxes only becoming visible in the final total?

2) Does OpenCart enforce the 'min_qty' requirement which I understand is the minimum order quantity. If so, where and how?

1. IF display prices with tax: no, then the subtotal shows the pre-tax amount and the tax is then calculated on the subtotal.
if yes, then then the subtotal shows the post-tax amount. Discounts should be displayed accordingly.

2. Min qty is populated from the product page and re-enforced on the cart page. If you set min qty 5, and add to cart from the product page, it will add 5. If on the cart page you try to change to something less than the min, then it will auto-correct the qty and give a message explaining that.

2. Min qty is populated from the product page and re-enforced on the cart page. If you set min qty 5, and add to cart from the product page, it will add 5. If on the cart page you try to change to something less than the min, then it will auto-correct the qty and give a message explaining that.

That's excellent. Now I can just pass on the quantity to Google and don't have to worry about the min_qty.

BTW.: The more I think about it, since the GoogleCheckout in OpenCart is like an express checkout, the whole order handling and fulfillment ought to be handled by the store owner via Google's Checkout Merchant Center rather than through the OpenCart admin panel. This way I don't have to worry about storing the order into OpenCart's database.