Thou shalt count to three. No more. No less. Three shalt be the number thou shalt count, and the number of the counting shalt be three. Four shalt thou not count, nor either count thou two, excepting that thou then proceed to three. Five is right out.
I don't know the number, but you can definitely brush too much. My sister in law was obsessive about brushing her teeth so much that the dentist advised her to lay off as she was damaging her teeth enamel.