possibly trim Finn’s reaction to the village and his “friend” being killed (i can understand him becoming overwhelmed, but he is a stormtrooper and you’d think he would be used to death)

That was actually Finn’s first mission as stormtrooper. It’s confirmed later in the movie when he confesses to Rey who he really is. He says to her, “On my first battle, I made a choice : I wasn’t going to kill for them.” So even though Finn was a stormtrooper, he had never actually killed anyone at that point in his life.