in my opinion, 5 units, with good morale, they can easily take down anything.
UPD: I can't figure out why in some campaigns, in the very first mission, they give an optional, but also impossible to complete, quest to choose the path of blood or tears. I cleared the entire map, but I didn't gain enough experience. Of course, if you ignore all the monsters and immediately grab a castle and recruit troops, there might be more timid monsters, but I think it's still not enough.