1. Yes. And actually any physical skill and normal atk can do shellbreak eventho if not monk as long as they have "shellbreak+xx%" things in their equips.
2. Hard to say. If you go high auto% the possibility to do s.break increase plus with high spam. If go for dmg, best of luck to do s.break but the dmg should be higher than auto%-focused build. For me i prefer increasing s.break probability.