Depending on what you're doing, I think you'll find you get better "tooth" for your powders using a mat coat.
Also, take a look at
http://www.earthpigments.com/ if you're going to be using a lot of pigments.
And if you're looking to get creative,
http://chestofcolors.com/how-to-paint-with-dry-pigments/ is an awesome article by Kathryn Loch on "painting" entire models with dry pigments.