With so many squadrons of units, would it be simple to add a function to assign multiple squadrons to one horn? A function for making one all-squadron master horn could also be part of this. This would give more control over a somewhat large army.
Also, having a horn command to assign all units to defense mode would be convenient as you wouldnt have to individually select units to walk around in defense mode. You could alter through the command table the defense radius the horn would signal.
Lastly, having 2 horns (and 3 if a defense horn is added) for different functions seems unrealistic and cumbersome. One horn per squadron/group of squadrons would suffice if when right clicked, a horn would prompt a small option menu:
Pressing 1 would ready units, pressing 2 would halt units, and pressing 3 would defense mode units. When the horn is blown after pressing 1, 2, or 3, each command would have a different horn call.