You have to wonder if the way his body is if he may have some pressure to his air sac that could cause the breathing? Or it could be over heating? What is the temp in their brooder? At 2 weeks it should be between 75-80 as long as their isn’t any draft. As for cleaning his nares I would think he’d do it when needed. Especially if he has water deep enough to dunk his head into. Are they mainly eating their feed? And the rest you mentioned is just small amount as a treat? Grit should be offered in separate dish and they will eat it as needed.
. Most of the time their mash has been eaten more than the veggies and i refresh it a few times a day as well. I was reluctant to offer grit desperately because I’ve talked to a few people and they’ve had problems with their indoor ducks throwing it everywhere and hurting their feet, hence why I add it to one, maybe two servings of veggies. Cuz Penny is messy and steps in everything and prefers to fling her food across the brooder 
