The way AI acts in the field doesn't change with the difficulty setting. They'll still go for the same targets, feast at the same time, and run away from 200 men when they have 800 scattered over 10 lords. mumblegrumble. Instead, the Campaign AI setting changes some numerical values, like the amount of gold lords get per week, troop wages, and
Scouting, Tactics, and Roguery can all be learned and used by your Companions so they are all useless to you making Cunning a bad stat and focus a bad idea. Charm, Leadership, and Trade are all good skills and you'll use them often at varying points in the game so definitely put stats in them, and for an optimal start you will already have lots hzds9.