World War I - Things I don´t understand
 

I don´t understand:

1) In a bombardment capable unit (mortar, howitzer) what´s the difference between the Shoot in Zone (Z key) and Shoot in Target (X key) options?
2) Do the depots are limited? Do they have a maximum capacity to replenish the units, or they offer infinite resources?
3) I could never use Alt+Z key. The Alt+R command I find very useful. What is Alt+Z for?
4) What is the difference ordering the units to move with the CTRL key pressed, the ALT key pressed and with neither. I couldn’t understand it.

If someone could clarify some of the points above, I would be very happy.

Best regards,