Here's a small thought. I've been playing French for the past couple of days, and I find the infantry troop tree a bit weird. The troops themselves are fine, but the upgrade branching is what irks me.
Wouldn't it make more sense for Grenadiers and Voltigeurs branch out of the Line Fusiliers, rather than Fusiliers and Grenadiers from the recruits, and the Voltigeurs out of the Fusiliers? I'm unsure of how it was in real life, but from a gameplay standpoint, I think it'd be better if you start off with the standard balanced troops, and then pick specialisations for them as they level up.
The same could be applied to the Light Infantry. IMO, the branching should go Leger -> Chasseur -> Carabinier/Voltigeur.
As for the Guard units, I'd prefer if the troop tree could follow the historical "progression", being everyone starting as a Tirailleur, then a Middle Guard Fusilier-Grenadier, and finally the Old Guard Grenadiers.
Of course, this is nitpicking at something not really relevant. It would make getting Old Guard Grenadiers much harder and expensive, though, but I think that fits the Imperial Guard.