congrats on your transitioning.
1. Yea henna doesn't really color your hair, I think it's more like tint but I saw at Whole foods that they have natural hair dyes.
2. Chemicals aren't good for any type of hair. But it's your choice on whether to color it. Some people would argue that you are not natural if you color. I colored my hair twice this year. I probably won't color anymore this year, just to minimize potential damage to my hair.
3. the white hair thing, idk. But try the natural hair dyes if it's bothering you that much lol