I really think battlefield is way too small to allow any real tactics. When there are 5 tiles between you and enemy, and some units can actually cross this distance in 1 turn, there's not much tactics to be done. I suggest you take inspiration from Master of Magic, where there are like 10 or 15 tiles between armies in the beginning and units usually move 1, rarely 2 tiles per turn...

Archers will make much more sense if battlefield is bigger, but then again they should shoot much weaker, too. They should also have limited ammo. Now they seem too powerful but at the same time it is easy for some units to cross the battlefield and kill them in two turns... that's not the role archers should have in "medieval" combat, which should be melee-oriented. Archers should slowly wear down enemies, not kill them in one shot.