That depends on your strategy and the available buffers. What do you need?
No, you need both of them I recommend you to read these tutorials to help you get the parameters:
https://fxdreema.com/forum/topic/4208/tutorial-06-my-indicators-in-fxdreema
https://fxdreema.com/forum/topic/9105/tutorial-working-with-ex4-ex5-indicator-file
Do you mean a subwindow or a new chart?