Having acted in this play before while I was in college, I refererred to the program and reviews from our production to point out a few things:
Brecht uses the Epic Style, which calls for disruptions between the audience's response and the story of the play. For this reason we had magnetized leaves which randomly fell from their trees to represent the death and loss in the play. We used additional music, song, and dance to develop character at unsuspecting times. There is also a campfire scene and, in our play, the campfire came on when an actor plugged it into an onstage outlet, in full view of the audience. Also during the the climactic fight scene, our director put one actor on a crucifix and paraded him across the stage as a reminder that people in the playe were dying for different kinds of "blind faith." In hindsight, that decision seems more controversial now than it did at the time.
The set was very open; since the play covers a broad time (30 years) it is probably best to let lighting suggest mood and place. The set pieces we did use were sparse and easily wheeled onstage and off. In our production Mother Courage's wagon wheels did not move - a decision purposefully made in the spirit of Epic Style disruptions. Our costumer also put bright red, "blood soiled" bandages on one character to represent wounds to the soul.
I think all three of the people would first have to look at how each of the main characters was affected by the war. This information is necessary whether you decide to write as a director, actor, or designer. Mother Courage gets her name because she tries to save her bread in the middle of the bombardment of Riga. She is so desperate to profit from the war that she puts this need above those of her children, leading to their deaths. Her two sons, Eilif and Swiss Cheese, are killed for their bravery and honesty, showing the senseless deaths of people caused by war. Kattrin is the daughter we feel the most compassion for. She can't speak and is scarred because of the war. Yet, she's a compassionate person and dies due to this quality when she beats a drum to warn a city of an attack. Yvette, the prostitute, shows how war takes away a person's dignity. The chaplain is a strong supporter of war, but he's also a coward. He helps prepare men to die, feeling the men should feel blessed to die for their religion.
For me, it would be easier to write from an actor's point of view. It's the job of the actor to get into the head of the character he/she is playing in order to be able to portray that character convincingly. The director would be more concerned about the play as a whole, rather than a single character. The designer might be the set designer or costume designer who would show the effects of war through the set or clothing.
Good luck! I hope I helped.