I have several listings like that and it is a lot of work to set them up initially, it is a ton easier after they are set up and generally encourages folks to buy more than one item at a time.
A word of warning...if you have a listing that has, say, 10 cards in it and sell 2, it will show as 8 available. When the listing ends and you go to re-list the item, it will show that all 10 cards are available for sale again. So, every time you re-list you need to double check and manually remove the ones that you've already sold.
Always looking for baseball variation/error cards and anything Garrett Whitley or Ian Anderson