In this post, I'll just talk about infantry. Cavalry and artillery need something as similar as possible to do the same job, but most of the work is done by infantry.
For now, Germans in Brigades of 4 stands, French in divisions of 6. Each unit has a clear command stand that also functions as a combat stand.
Size is automatic and not really distinct -- it is just the number of stands. However, some rule may be needed to detach some stands, or to allow for the unit to be badly spread out.
Resolve will measure willingness to attack or hold. Events in the battle will decrease or increase resolve. A unit (army?) will have a starting resolve and a maximum resolve. Units will have to test for control at various points. If the resolve is too high they may attack when not ordered to; when the resolve is less than some value they will become reluctant. At zero (perhaps) they will break. This should be the only number we need to track.
I think we can get by with just one -- Posture, which can be route-march, offensive, defensive, or routed. Keeping routed units on seems a good idea, since they did tend to clog march routes and add friction to releaf or withdrawl.
Is formation a state? I suppose so, since it is a limited set of discrete values and rules for moving between them. Formations could be used to indicate posture - 1 rank defensive, 2 ranks offensive etc. It could also have a continuum of values in which each stand has its own facing -- or perhaps that is a part of a defensive posture.
There is a temptation to give the stand a fair amount of latitude to match what battalions were up to in the smaller battles - but eyes on the prize, it's what the brigades and divisions did at the big battles that matter.