Use a mix of baking apples, such as gala and Granny Smith.
Pie can be stored, covered, at room temperature for up to 2 days. For longer than 2 days, store in the refrigerator.
Not all gluten-free flours are created equal. In fact, they vary greatly. This recipe calls for a 1-to-1 gluten-free flour blend. There are a few different brands out there, and I've used both Bob's Red Mill and King Arthur Flour cup for cup or 1-to-1 flour blends. Look for a blend that says it will work as a complete swap for all-purpose flour. I have not tried this with any other gluten-free flour besides the two listed above.