#1 most important would be showing whether a unit is a Keil or not. This is important to know when positioning your cavalry, and it's annoying to have to mouse over units every turn to tell, especially since units can lose the Keil status due to casualties.
#2 would be an icon telling that a unit counts as Light. This is already reasonably easy to tell, but an icon would make it easier to identify flank threats at a glance.
#3 would be a Disorganized marker. Rough ground is not always obvious, especially when a unit is standing on it. Maybe it could be yellow for moderately disorganized and red for severely?
As has already been said elsewhere, some kind of indication what units can still move would also be nice. Perhaps units that have not been moved could have a glowy border around the flag?
Something like this:
