How I play officer is switching buffing/healing/etc
Whenever things are off cooldown, I switch to Officer, use them then switch back to engineer. That seems to work the best atm. Probably even more so during raids. The ability to do engineer roles while mid cooldowns for officer is pretty nice. Not sure if they will fix switching roles or not in the future.
The ability to heal and buff your troops often is helpful as if you dont pay attention to them, they will sometimes die.
Stances: I set them to offensive- 2H in most cases as they do alot more damage. Though at times when I really need to pay attention elsewhere, I set them to defensive so they take less damage and tends to be safer for the heal switching.
Target priority: I always set to target Sappers because those buggers will ninja your banners and burn them. One less thing you have to worry about during the fight,otherwise you have to constantly track your banners to make sure they are not in need of repairs. I've failed Full Plat runs before on the main quest because ONE banner was burned and was literally 1 point from full platinum.
Armor Stances: If you play it right- Engineers keeping the enemy catapults in check- as well as switch healing/buffing every few minutes, these dont really matter. I havent had to pay much attention to it so far and hasnt been severely penalized for it.