1. You have protein sensitive hair, that is why it's dry. Deep condition, oil treatment, etc. It will retain these treatments well so don't worry. Also amla helps. Amla is all you need with henna in regards to adding something acidic if you have protein sensitive hair. 2. Gray hair is a challenge. It will be very orange. I suggest if your goal is auburn, to mix indigo with it. It will make your gray retain deeper color. 3.Your hair will darken for a few days then it will fade. If you want to hold and build an auburn it takes awhile, but it's possible.