Ive looked into this one myself, i do some coding and my plan of attack is
Basically if you want to automate a online shop, first of :
1. Look into the shopping cart, Virtuemart.org, which is runnig on Joomla
2. There is a funtion for automated .csv uploads. Which means, you have to configure a .CSV file with all the specs _sku, _product_category, etc etc. And once you've made a good one of those. Take contact with the supplier and see if they can send you your custom made .csv file to a specific source, loaded with the info you need, after that you make a scrips(sound easy but, hehe i got stuck there), to upload it to virtue mart, and that itself configures your site with all new products from supplier, pictures, etc.
And then , once that part is done, youve got a autoshop, then just automate so when you receaive payments through paypal, and the money is in you acc, it sends a form to the supplier with delivary info. Makes sence ? maybe we can work on something together..
i dunno, give comments tho