You could use yeast instead of baking powder.
no
if the recipie says to use baking powder you should use that as that is how it is sopose to be used but you may try and use baking soda if you don't have baking powder
No.
Using Baking Powder Instead of Baking Soda* You need to use 2-3 times more baking powder than baking soda. The extra ingredients in the baking powder will have an effect on the taste of whatever you are making, but this isn't necessarily bad. * Ideally, triple the amount of baking soda to equal the amount of baking powder. So, if the recipe called for 1 tsp baking soda, you would use 3 tsp baking powder. * What I do is compromise... I use twice the amount of baking powder as baking soda (add 2 tsp of baking powder if the recipe calls for 1 tdp baking soda), plus I omit the salt (which adds flavor but also affects rising in some recipes).
nothing really
Baking soda will cause things to rise also. Muffins are smaller so there is not as much need for lift. Baking powder will give more rise than soda. Whoever created the recipe chose to use soda instead of baking powder.
flour
you can use cornstarch
Yes. However, if you use baking soda instead of powder, you'll need to include some acid. A teaspoon of lemon juice or using buttermilk instead of regular milk will work.
There isn't one. Bread Soda is the Irish name for baking soda.
Baking soda does not rise as well as baking powder