brushing the hair at the scalp can stimulate blood flow in the scalp (where the hair follicles are) which can promote hair growth. Brushing too much or too harshly though can cause breakage. Instead of brushing excessively you can brush as needed and gently, and then give yourself a scalp massage or take biotin.
No, that's a myth. Hair is dead except for where it attaches at the roots on your scalp so brushing it won't make any difference, you may just end up with more breakage. Just condition to keep it healthy as it grows out and eat a healthy diet, there's really nothing you can do to make it grow faster.