that coop has got a lot of wasted space currently. What I would do is add more perching bars above the original perching bar going across. to fill that space. Means more chickens can sleep in it too. Laying boxes don't need to be anything fancy if it is temporary, just somethimg easily accessible. I have seen people use buckets.
I think it has plenty of ventilation. I wouldn't want to add any more, maybe just one vent at the top to prevent stale air building up there
Chickens don't stack for storage.