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As an easier alternative to Rovereto, I would suggest a day trip to Bassano del Grappa from Venice. Bassano is only an hour and ten minutes by train from Venice, and it's a wonderful, small city steeped in World War I history.

In the historic center of the city, at one end of the wooden footbridge (designed by Palladio) across the Brenta river that is Bassano's most famous sight, you'll find the Museo degli Alpini, a small but very evocative museum of the Alpini, the mountain branch of the Italian military. There are many uniforms, weapons, and other artifacts of the Great War, and the entry fee of one and a half euro includes an audioguide, available in English. The entrance to the museum is inside a bar called Taverna Al Ponte. This museum doesn't have an English-language website, but if you scroll down the page on this Italian site, you can see photos of the museum's displays:

Alpini Museum

Also in Bassano, about a mile's walk along the Brenta river from the city center, is the Museum of Hemingway and the Great War, which is in the Villa in which Ernest Hemingway, John Dos Passos, and other members of the ambulance corps of the American Red Cross were stationed during the war.

Museum of Hemingway and the Great War

Both of these museums are closed on Mondays. On your way from the train station to the Alpini Museum and the river, you'll pass through Piazza Garibaldi, where a bas relief map on the side of the large church shows where hundreds of bombs landed in Bassano during the Great War. Nearby Monte Grappa was the site of heavy fighting between the Alpini and the Austrian army. Unfortunately, you need a car to get up there, but at the top of the mountain there's a dramatic ossuary/monument containing the bones of 12,000 Italians and 10,000 Austrians who died on the mountain during the war. There's also a tunnel into the mountain, left from the war, that you can walk through (ask at the museum there for someone to let you into the tunnel).