A very long post - I will need to consider before replying on the conceptual level. I am a bit of a WW2 buff and I do fit into your over 40 crowd. I grew up knowing men that were fortunate enough to return from the war, some of whom actually talked with me about some aspects of their experiences.

With regard to the question in your second last paragraph, one veteran I spoke with was assigned to a tank detail when the Allies invaded France. Infantry (either parachuted or glided into the area ahead of the main ground forces) were stationed at the sides of city streets providing key defensive coverage using Bren machine guns. These were well suited to prolonged firing with a flared barrel, however burnout was a concern so (as you indicated) the gunners were trained to use short bursts. This was important for more than just preserving the weapon though. Certainly accuracy was increased since there would be substantial kick from these weapons and with the two support feet at the front, the guns had a tendency to skip side-to-side. More importantly, ammo was limited and wasting shots would soon render the position useless. The person that I spoke with had the task of dropping steal ammo canisters to these gunners as the tanks passed by.

I think that Wolfenstein - Enemy Territory had a style similar to the way your team member is describing for the Sten and the Churchill tank machine gun. As I see it, you might be able to come to an agreement on this by combining your ideas in such that prolonged usage will require a "cool down" period. If the cool down is ignored, the gun would soon stop working and the player would be forced to change out parts. With regard to limiting ammo, parts, etc., the game style dictates the direction. Leaning heavily to the sim style would dictate that supplies would be limited. This was the reality.