Some people have tap water that contains quite a bit of nitrates in it. Those people tend to use K2SO4 instead of KNO3 for their potassium, to avoid going too high in nitrates. Other than that, you have the ones that are needed. If your water is relatively soft, or your water quality report doesn't verify that you have some magnesium in the water, using GH Builder is also a good idea.
You can dose the powders by just dumping them in the tank. Don't worry about the fish appearing to try to eat them.