Awesome he's eating. When my cat Maggie was 3 months she had no trouble eating but when she was adult she kept walking away from her oval bowl so I got a whisker free bowl at a small pet store $20 and she started eating. She does have long whiskers. I also bought online 3 big ceramic bowls whisker free for water. They are big and they tilt. Now my my cats drink more.Adult food that he will eat is better than kitten food he won't eat.
Perhaps he doesn't like the bowl and does like the plate. Some cats don't like bowls because they brush their whiskers on the side. At his age he might not like the bowl because he can't see over the edge while he's eating.
Air vents, all air vents, send dust out with the air. So, yes, that may have been why he coughed. You can put filters in the heating and air vents, but I'm not sure you could do that with the smaller one in the computer. That vent may need all the area it has to function.