1. Most of us find it MUCH easier to not mix it in the full 8oz of juice; it is okay to mix it with just 1/2 cup of juice (more or less). Just shake/mix it really good, and make sure to have 8-16 oz of water after each dose.
2. I think (especially since you're only taking 20 mg of Valium) that it would be best to start at a heaping 1/2 teaspoon 5x daily, rather than a full heaping teaspoon.