Agree on the salt dosage, 1 per 5 is plenty. For WC's I would have done a larger 50% change right away, then added salt, then 25% every 2-3 days adding enough salt to compensate for the new water each time.
He seems to be the same this morning. Just laying on the bottom breathing really hard. Should I be worried about how hard he's breathing? I figured it was from the stress of being nearly completely dried out except for the gills
Nothing you can do other then keep him clean and warm, let him recover.
Good news is In my experience the first 24-48 hours are where the death occurs. If he's made it this long his chances of survival are already way up, the heavy breathing should subside as he recovers and regains his slime coat, as long as he isn't getting worse the best thing you can do is just let him rest. Sitting on the bottom is good, it's when they start hovering at the surface that you know somethings wrong, so if he's staying down it's another good sign!