You get 1 pic per card! They really don't even look at the numbers, just glance to see if it's a Disney card.
Yes, go to Ariels Grotto before it opens and the Disney photographer takes your pic and they give you a coupon that you take to the photo shop and redeem for your pic. And you do not have to pick that photo, you can choose any photo that Disney takes in the parks.
So if you have multiple cards and you go every day of your trip you can get a lot of different pics
And we must have went during a shift change cause we got Mickey, Goofy, Chip and Dale all in our pic