Some of this is getting into the realm of what did they really do. The 3,600 rounds was a swag based on information I found with respect to what M-60 machine gun teams supposedly have done. Ammo can be removed from the cans and carried around the neck, but I don't know if the Germans did that or not. It certainly has a down side of getting the ammo dirty and possibly jamming the gun. It would be possible to carry more ammo around the neck because it keeps the hands free, assuming they weren't used to carry more ammo
This area could be beat to death. How about a German 81mm Mortar Group moving two mortars, 80 rounds of ammo and personal arms? How much did a mortar round weigh? The lightest American round was 6.87lbs according to Wiki. Assuming the German rounds were in that range, counting the two mortars, you have each man toting 100lbs each, before you count personal equipment.
Z Fire in the game is used often in a fairly gamey manner, aided by our overhead view of everything. It is one thing for a unit to Z Fire at someone they saw move to a concealed position, but entirely different if it is used because someone 1km away, without a radio, saw them. It is just the nature of the game. Some realism has to be sacrificed for playability.
In reality, they probably didn't pepper areas unless they had personal knowledge someone is there. That is the whole idea behind tracer rounds, so they can tell they are putting rounds where they want. They go out the window if you can't see the impact site. Maybe doing away with Z Fire for locations out of LOS is the answer. The AI doesn't use it anyhow. It could still be used if you can see the target hex, without specifically being able to see a target, but otherwise do away with it. You still keep splash for out of LOS areas to account for ricochets. More than one person has been killed by them.