I found the below link helpful in terms of learning about Henna and Ayurvedic hair care. It is targeted to Salon owners, but it's useful for anyone.
So far, I have used Henna, Amla and Brahmi Powder. I have also used a few different oils such as Vatika, Shikakai and Parachute Coconut Oil.
As of now, the only product that had negative effects on my hair was the Vatika Oil. Let me just say I was shedding like a dog!
I have found that the powders made my hair stronger and they remain a staple(Henna and Amla Powder) in my regimen although I don't use them as often as I used to.