* How (or will you) is leadership defined in a unit? In all military units there is a chain of command. Will units have a breakdown of what leadership skill levels are present? And how will rank be factored in. Rank trumps leadership for control, at least in reality. You could have a rank-5 with leadership-1 and a rank 2 with leadership-3. So, in theory at least, the leadership check for the unit would be done using a leadership-1 DM. The same would go for tactics.
Leadership is covered under the Force Organisation preview - basically, every unit (of whatever size) gets appointed a leader, even if it is Joe Bloggs Rifleman (we recommend it is not).
* Since we are talking about mass battles, assuming you have multiple sections (infantry, artillery, assault, etc), will the individual units take into account specific skills that are related to their actions. For example, you have a company that has three mortar platoons attached to it. Platoon #1 is standard platoon (so maybe no DM's?), but Platoon #2 is veteran, and Platoon #3 is elite. The leader of the company (Leadership-1) gives a fire mission command to all three platoons. Would you have individual DM's attached for the different skill levels of the platoon's? Or would their skill levels not matter? At what level do you split this out?
Up to you, the level of detail you want in the batle, and the wishes of your players. In the above example, you could combine all platoons, taking the majority for skill level and adding the mortar platoon as the Support trait if there are sufficient numbers (see Force Organisation again). This could work if you just wanted to quickly resolve a battle 'off-screen' as it were. Alternatively, if the battle was the focus of play, split the company down into individual platoons - there are only four of them and it will be no more work to play out the combat than if there were just four guys on one side in a nral firefight...
* As I mentioned in a previous post, a unit at 50% casualty rate (dead or just wounded), does not operate at 50% capability in the real world. Unless they were fighting for their lives they would cease to be seen as an effective unit and would be pulled out of the fighting. The could conceivably operate at 50% effectiveness on defense, but certainly not offense.
Morale checks have to be made as the unit takes casualties and as for effectiveness, this is covered by outmatching. A regiment sustaining 50% casualties will not likely retreat before a single squad, but will be shifted by another regiment that is fresh. Remember casualties are not automatically deaths - see the recovery rules.
* Will you be including defensive bonuses here? If a defender is entrenched or has fortifications, they enjoy a force multiplier of their own. Which is why attackers, who enjoy a bonus initially since they get to set the pace and target, always have to outnumber defenders, or at least out-power them, if they expect to have a chance at victory. Also, some units (infantry) excel at defense, and others (armor, artillery) have high offensive values but very low defensive ones. Will these be taken into account? Perhaps when building the unit they would get these numbers attached to them based upon their unit structure? Building up larger units (BN, Brig, Div) would also have their capabilities dependent upon their sub-units, which should somehow be reflected in their unit build strengths/DM's.
Some of these might be worth a look, but many of them are already built into the rules. Troops in defensive positions will already be gaining the benefit of cover (ad morale bonus, for that matter), and so will have those advantages in combat anyway. Armour and artillery (and vehicles in general) have not been added to the rules yet, but you can imagine them acting in much the same way, grouped into units of a single vehicle, squadron, company, etc, as appropriate. Artillery should not be anywhere near the front line, but if it gets caught out, its existing stats will take its deficiencies into account.
That is the key here - use as many existing rules as possible.
* How will you take into account highly mobile (grav) units vs. ones that aren't? A grav unit on the defense can easily outmaneuver a much larger unit of say tracked or wheeled vehicles.
Again, as has already been pointed out, it can dash anywhere it wants to on the battlefield whereas, in comparison, tracked vehicles will be effectively immobile.
* Unit morale should also be accounted for (recruits, veteran, elite, etc). This is, or should be, the single most deciding factor for morale checks. Elite units can exert a far more powerful presence than say a unit made up mostly of recruits.
Again covered by the Force Organisation rules (also on Planet Mongoose).