Hello! I would like to present some links below that may help you complete your research.
Seney- this link talks about Seney and Hemingway's connection to "Big Two-Hearted River."
Coming of Age in a Lost Generation: Nick Adams, Ernest Hemingway, and the American Bildungsroman Tradition- there is some good information here about the war trauma that affected the Lost Generation young soldiers of WWI. The Bildungsroman is usually a work describing the maturation process or coming of age of the main protagonist. You might say that "Big Two-Hearted River" is a bildungsroman. Just like Nick in "Big Two Hearted River," Hemingway was wounded in WWI. This article documents what Freud calls the "war neurosis" of these soldiers, and talks about the fatigue, depression and insomnia the soldiers experience in the aftermath of WWI. While this is not strictly a "Big-Two Hearted River" resource alone, there is a lot of information you can use regarding the war trauma angle for your project.
Big Two-Hearted River: Survival and War-a very good link with some historical background, war trauma discussion and literary analysis.
Hope the above links help. Thanks for the question!