A: Yes, SHOPPINGCART.ORG products support inventory control. User can restrict in-stock quantity by simply defining the number in stock for each item. Cart won't allow to purchase more items than there are in stock. In addition, for you to have life in-stock qty update functionality (i.e. for the in-stock qty number to diminish after each purchase) you have to have an additional IPN plugin: http://shoppingcart.org/catalog/store/category7.html