Baking soda. Simply heat baking soda or sodium bicarbonate in a 200ºF oven for about an hour. Carbon dioxide and water will be given off, leaving dry sodium carbonate. This is the soda ash.
No; good question because this is a common misconception! Baking powder does have baking soda mixed in it, but it also has a powdered acid, such as cornstarch or cream...
Yes, that's actually much easier than doing it the other way around. How long it takes depends totally on whether your hair was dyed brown in the first place, though.
Yes, although you should talk to your stylist about potentially adding other layers or working in different sessions depending on the texture and color of your hair.
