Baking powder is definitely allowed in the first stage of the diet, I use it to bake my coconut bread. Make sure that it has no aluminium content or traces. Thats as far as baking powder goes. I can safely say that baking soda is also allowed, once again be sure that it contains no bad stuff. Tryo to look in the search, key in a topic, im sure you will find lots of info.
Hey good luck