Mash the rest of the beans with their liquid. Heat at least 10 minutes to blend flavors. I'm not sure why the recipe doesn't call for you to cook a smaller quantity of beans, rather than spooning out the cooked beans. The pamphlet says that you can make the excess beans into a salad by covering them with French dressing and refrigerating. I think they're trying to sell more beans.
Chili powder is a spice from Texas and Mexico consisting mainly of ground dried chili peppers.
Green chili salsa is a Mexican condiment made from hot green chilies, onions, vinegar, salt, and other ingredients. The slow soak method gives beans a better texture. Since these beans will be mashed, it won't make much difference, unless you're concerned about those 3 extra cups of cooked beans you will make into a salad. No need to measure.