In a recent Channel 4 (UK) survey of the top 100 war movies Steven Spielberg voted this as his favorite, mainly due to its sheer "boys own" factor of unreality. He even went so far as to repeat the "Broadsword calling Danny Boy" line.
The bus stops after the bridge so that it can be booby-trapped. Yet the entire road up to that point had been elaborately booby-trapped. They could have even just briefly stopped and dropped a couple bundles of dynamite in the middle of the bridge with a 15-second timer so that it blew the bridge as they drove away. It made no sense to stop and booby-trap the bridge during the getaway, as it cost them valuable getaway time. But it did add valuable tension to the getaway.
The common weapon in the movie was the MP40, a German submachine gun. Thee MP40 could fire 500 rounds a minute, and had a magazine capacity of about 40 rounds. In several places in the film, characters fire for extended periods, and yet no one ever has to reload.
While the presence of signs reading "Militärkommando Hohenwerfen" in the castle would, at first glance, appear to be an error caused by using the actual name of the shooting location Schloß Hohenwerfen (called "Schloß Adler" in the film), similar signs can be seen on other buildings. This indicates that "Hohenwerfen" does not refer to the castle, but to the administrative region (e.g. a municipality) that contains both the village of Werfen and the Schloß Adler.
Did the Germans really have helicopters in World War 2?
Yes, the Germans used a small number of early helicopters in late World War 2 for tasks such as transport and artillery spotting in addition to numerous experimental prototypes. Two Fa 223 Drache ('Dragon') aircraft were actually assigned to the German Army's Mountain Warfare School at Innsbruck so the prescence of a helicopter in the film is surprisingly plausible.
Who killed the 2 other members of the team?
Presumably the trio of double agents killed them because they were suspicious of them and had seen or heard something that betrayed their treason.