Sorry to barge in mid way through your dialog.
I was looking at this contrib thinking it may be useful but if I add an item to an order how will I get payment for it? I use Barclaycard Business EPDQ CPI as my payment provider (in the UK) and they handle all the CC payments. Without contacting the customer for their CC details all I can do via their site is issue credits, void/delete etc. I can manually process a payment only if I directly contact the customer and get his CC details, which kind of defeats the whole e-commerce thing....