If adding extra dry ingredients to a recipe, how much extra water should I add to compensate for their effect on the dough?

I routinely put in small seeds such as linseed, hemp, buckwheat sunflower and pumpkin with no real impact on the bread. But I also have some whole grains of oats, wheat and barley that I want to add as well, but I am worried that they will draw moisture from the mix, making the loaf too dry.

Should I soak these first, or just make a wetter mix and allow it to sort itself out?

I like a seedy loaf, and the more in there the better, but don't want to spoil things by going to far.