Put the cereal in the bowl of a food processor fitted with a steel blade. Process until finely ground. Add the gluten-free flour, tapioca starch, sea salt, and paprika. Pulse until combined.
Spread the diced butter around the flour and pulse until the butter has worked itself into the flour mixture and is the consistency of small peas.
Mix the water and vanilla together. Then, add the mixture to the flour and butter mixture and pulse until combined. (The dough will be wetter than a pie crust).
Wrap the dough in waxed paper and chill for at least one hour.
Preheat the oven to 400 degrees F.
Divide the dough into 4 sections. Flour each section before rolling it out between two pieces of parchment paper. Roll to ⅛-inch to 1/16-inch thick. When desired thickness is reached, peel off the top layer of parchment paper, lightly flour the dough again, and set a baking sheet on top of the dough. The back of the baking sheet should be against the dough. Flip the sheet and the dough over, and then peel off the remaining piece of parchment paper.
Use a ruler and pizza wheel to cut the dough into 1½-inch squares. Sprinkle with salt, if using. Bake for 5 to 8 minutes. Let the crackers cool completely on the baking sheet. Repeat with remaining dough. Store the cooled crackers in an airtight container at room temperature.