Yes, the stevia that they sell is great. It is the raw, green stevia.
As far as the greens, what I do is create a mixture of the greens. If I had the above grasses plus spinach, I would take equal amounts of each (say a tablespoon or 2 of each one I had), and combine them into a container or baggie and mix well. You may want to reserve some of what you buy in case you want to adjust the recipe later.
You should try to drink a liter of water per 40 lbs of body weight per day, and I would suggest that you prill the water and put a teaspoon of the mixed grasses in each liter. You can also put 2 or 3 drops of the Miracle-Mineral-Supplement (unactivated) right into the mixture to increase the alkalinity of it.