Oh but wait, I think when you load the sprite image from url, it will change the image for every sprite on the screen, not just one particular instance. So you still would need a many, many unique sprite instances for each different card. Damn I think this kills it.
We need to be able to create an instance of one sprite, call it "cardSprite", then load that cardSprite instance image from the file and not change the image of every other cardSprite instance.