Adwords and Ecommerce

Have anybody used adwords for ecommerce? I have mainly used for lead generation. The thing with adwords is 1click/conversion and many clicks per conversion.

i, How to set up such that if the customer clicked an item and added many items I can determine the value of the items added in the basket.?

ii, How do you calculate how much you can test before you shut down a keyword eg. in lead generation I use formula 2*payout and check to see returns.

i, there is no such feature. Adwords can only track if there was a conversion. Not how many or the total value.

ii, most people calculate the ROI based on spend and revenue. A negative ROI is not good.