Alrighty. I have been reading up on the mass combat rules as well. If we have the existing commanders of the army (lower officers and such) direct the troops that will free us up as a contemporaneous, yet separate and manageable theater of the battle.
I will look over the stats, but it would seem that using the ranged option prior to melee is warranted since we have the consumption cost of the ammunition covered. Then in the melee phase use the Cavalry Expert tactics to increase the OM. That with the size of the army should produce a relatively quick victory with the ranged attacks, hit point advantage and OM from Cavalry. That will more than compensate for and DV advantage the tieflings have from terrain.