So returning to this, on consideration my goal isn't tactical movement, though that might be a way to do it. Some possible ways of doing it:
1: A movement-based approach. Divide each day into 4 (ish) 'turns'. Each unit has an initiative modified by a commander's tactics skill. They can attack everything within the same square (a very large area). All units on side A roll as one entity against all those on side B.
Problems:
A: When is combat resolved in this case? It seems problematic to resolve it multiple times per turn. Also, the casualty table would have to be modified. Perhaps the answer is resolve everything at the end of the turn, but once an enemy moves into a square a skill check (opposed?) is required to disengage and move to another square?
B: What about artillery and seige equipment. I everything up to modern artillery would have a range that would force it to be in the same square as a target. An upshot of this is that your system can simulate wars with muskets and cannon--not relevant to the Farland CS, but a worthwhile point. On the other hand, cannons (or balistae) can't chase people down. Perhaps attach a penalty specific to that to that sort of thing.
-This adds a really irritating amount of math that under the current rules since CR and number bonuses are relative. This is actually one of the weaknesses of the system (as misused by me). It would help to make a table of flat bonuses and penalties for CR and numbers. (Set a baseline at CR 1 and 1000 troops, say?)
2: A 'resolved all at once' approach. Each unit designates one other target, or an objective/area to defend (a city, a hill, the 1st Legion, etc). This determines who attacks whom. To prevent excessive ganging up on one unit, tactics rolls may be in order if you bring several units to bear on one target. This has the benefit of resolving everything at once as-intended. You lose some of the tactical richness though. Also, it would still benefit from a fixed rather than relative table of CRs and numbers.