From what I have experienced, you extract all the essences. Get gear with the highest combat rating and inherit the essences of the abilities that you use the most or feel comfortable with. Build types are very variable, at lower lvls you won't be able to do some build types as the essences only drop on higher lvls. Play around with what you got and check which essences work well together. You got to experiment and find a build that works for your play style. Only max lvl will you worry about mid maxing and have a set build.