Here's some of our preliminary thoughts on checkout and shipping.
Each of our fulfillers and product types has a variety of different shipping calculation methods and shipping vendors. We'll simplify these to make three options available at checkout, economy, standard and express.
Each product type will be handled by a particular shipping module, which will base shipping cost on whatever parameters, e.g. shipping zone and qty of items, or zip code and weight of items. Each shipping module will also create a tracking id for its portion of the order. The shipping prices will be summed to calculate the total shipping cost. But, individual shipping costs for each part of the order will also be saved (along with tracking number), both for purposes of displaying to the user and for accounting reasons. Here we can also saved the exact shipping type/vendor selected by the module (e.g. USPS express or FedEx Overnight)
This post will be fixed/completed if I can uploads working on this site ;)