The size of any of the polities in the Vargr Extents should help with #2.
As far as #3 goes, a loose comparison against Soc for the Nobility in the Imperium might also help with figuring out a mechanism that mechanically calculates the optimal number a pack leader can lead. The thing is, I don't think there should be an 'optimal' number for Charisma when used for Leadership. I say this, because if there were 'Optimal' Charisma Leaders, it would go against the Vargr lifestyle of leaving a low Charisma loser(?) for a high Charisma winner(?). Besides, wouldn't Optimal for Vargr be from the viewpoint of those being led, not the leader?
Context would be required.
This is, as always, half groping in the dark, as to how fictional space race civilization functions, even with the canine connection.
At the micro level, we're dealing with a platoon sized bunch of wolves, who require direction, and the mechanism for that is confidence in a charismatic character.
I forget where, but the pack is supposedly between twenty four to fifty individuals.
The more charisma a pack leader has, the more confidence the pack has in him, and the larger the pack would, or could, become; this is balanced by diluting the effect that the increased charisma has more more packmembers.
At the same time, if the numbers are a tier below at subpack level, the charisma is more concentrated, and loyalty could become fanatical.
Adjust and modify by any number of circumstances and skills.
At micro level, this should be rather simple to calculate.
Optimal being more of a yardstick, for when the pack grows too large to effectively control; personal circumstances for a packmember would decide if he stays or goes, part of which would be the pack leader's charismatic effect.