The ranch setting had a huge impact. It was a place of isolation and hard work, which influenced the characters' dreams and relationships. The bunkhouse, for example, was a cramped space where the men lived. This closeness led to a lot of tension and competition among them.
The class structure within the ranch affected the characters. The boss held power over the workers, and this power dynamic created an environment of fear and subservience. George and Lennie had to constantly be on their guard to keep their jobs, which influenced their actions and decisions throughout the story.
It's a novella. The length and complexity of Of Mice and Men classify it as such. Novels tend to have a more extensive scope and development, which this story doesn't quite reach.