About archers targeting other ranged units, I'd like them to normally target the nearest unit, but when you tell them to attack a unit, they should go on to attack other units near that one after they kill it.
Meat shield infantry and range dps should continue to be major roles, but I'd like more diversity among units, so there would be more other roles, different ones specialized in different ways. Pikemen could be a more specialized melee fighter, weaker in pierce armor, swordmen stronger in pierce armor than melee, a range unit or two should be more armored instead of only differing in attack and range; the elephant archer of course, but I think the skirmisher (peltast) should be too. There should be a couple melee units that have high attack and less armor, like the axe and mace men Kush has, and a cavalry.