Could be he just got a little food or something in the airway. I'm glad you are hearing improvement.
You can give small treats of mealworms or veggies/produce a few times a week. For growing chicks, I usually focus on them eating the Chick Starter for the majority of their diet, but I still like them give them bits of something else too. It's fun for me and I think they enjoy it too.
Well, don't pay me any mind about guessing genders or breeds sometimes.
I don't think that is a White Leghorn though, too "sturdy" looking. I don't mean that in a bad way, this one just doesn't have that Mediterranean look. I could be wrong. Maybe a Rhode Island White or White Plymouth Rock. As he matures you'll be able to tell more.
But I do think he is probably a he, but time will tell on that too.
And of course, I could be very much wrong on that one too, not the first time. I had some Barred Plymouth Rocks and could not decided for months who was male or female on a couple of them. Man, that was a total puzzle for me