<Apologies if this is a repost - I had fallen off line when I attempted first posting>
(Quotes from all over the place)
The game idea we're going for is perhaps most reminiscent of Peter Turcan's Austerlitz and Waterloo; though hopefully much more user friendly to play, more easy to understand, and much more fun.
I must admit, I always liked the idea behind Turcan's Austerlitz. You see no more than what Bonaparte could see, you send orders which took time to be reacted upon (if at all), you were not commanding automatons that moved exactly when and where you wanted.
His engine seemed to predate mouses though. It seems to me that one of his worst features was trying to set (or reset) a battle line (plus the requirement to word orders exactly, and the artificial limit on orders per turn). Clicking and dragging/drawing would possibly improve this process.
I was thinking about the way in OFP can use the map to set objectives etc, but as your system will include troops occupying an area - probably in a well defined shape for the legions and phalanx - maybe the appropriate analogy would be one of those software packages that let's you remodel/change furniture for rooms in your house. However, it is difficult to think of some of Hannibal's celts in nice regular shaped formations.
(I believe that Turcan is back in the saddle doing another horse and musket game with a French name like Bataille?)
I must be strange - I don't want complete control over troops in battle, I don't want complete control over the country (and with a large delay in finding anything out) and I have little faith in being able to maintain a dynasty.
Finally, way off teh point by now, but one of the worst modelled aspects of military campaigns seems to be logistics. From a comprehensive survey - alright Caesar's Gallic Wars and Engels Logistics of Alexander - supplies for campaigns seem to come from where you are going rather than where you've been (unless you had a navigable river). I don't mean foraging as this would slow an advance down too much - what seemed to happen was that areas on a line of advance would be 'organised' to provide supplies. This would be as part of a surrender process, so if the enemy was near you either sought them out to force a battle or you retreated
I think* Engels said that horse drawn transport would eat everything it carried over a period of three days (with no foraging that would of itself slow down the train). Further staying still with a large force would quickly exhaust an area's foodstocks.
* OK I checked.

Random battle maps
Though possibly we'd see 'common' generic maps such as Thermopalai, Chaeronea?
Armies move on the operational strategic map in seasonal turns. Each area is given by a terrain type. When armies collide, a whole lot of stuff happens: ...
My first impression is that your following description looks a mix of miniature and board gaming systems - not a criticism, just interested as to how it will work.
Will armies collide, two examples out of this period but only just - Would Issus be possible under this system or was teh situation a bit specific - Alex goes one way down the coast, Darius goes up the other side of teh mountains and comes from behind. Alexander did not know where Darius was prior to his appearance behind him. They meet in a narrowish valley. While both seemed to want battle, it is hard to see how either could have kept their army together if they declined battle. Apologies for simplistic description. (or if wrong). Similarly, oh what's it called - the one where big Juli got caught by the Belgae before he had time to set up camp. But here you have a very good general, by his own admission, basically ambushed because he was unaware of his opponents presence.
Sorry, long again and rambling