You can change the size of the empanada, just adjust your cooking time up or down.
The ratio of the zucchini, squash, and eggplant can vary. You are aiming for approximately 1/2 pound (8 ounces) total between those ingredients.
You can use pie dough in place of the empanada dough. This is the empanada dough I use. If you use pie dough, you will need probably 2 or 3 “crusts” depending on how big they are. I prefer to make my dough because it is incredibly quick and easy to do!