For the battle of Corinth, you are allowed up to 15 units. Infantry brigades (good-rifle/melee mix) with a couple of strong melee cav units works.
You start at the top of the map and face, to the south, a long east-west Union defense line guarding a flag.
It is not very challenging. Lining up on the E edge of the map and marching west to the flag generally works.
Once the flag is taken, CSA units can form a wide perimeter around it, using cover. The Union will counterattack but only half-heartedly.