Yes! Oat flour is a great substitute and will make your finished product more moist. You'll need to adjust the recipe, however; for every 1 cup (100 g) of all-purpose flour, use 1 1/2 cups (150 g) of oat flour.
An all purpose flour, gluten free or otherwise, is just that, *all* purpose. Bread flours have a higher protein content which provides better gluten formation. Psyllium husk is an option,...
That is the choice for this particular recipe; it saves time and makes the combining of ingredients slightly easier. However, it's a personal choice and you can find an alternative...