I would think 6 bantams or 4 standard chickens would be fine. It has ventilation openings so their health shouldn’t be a problem. I don’t know what the building materials are so how well it holds up may be a question but as long as it does I’d bet there won’t be any health issues.
No idea the weight it was so many years ago but it was a double yolk the size of a large duck egg. I know it was double yolk because I dropped and broke it carrying it into the house! The dog enjoyed it.
Possibly stressful if you have some of the more nervous breeds but probably not even with those. I’d be more worried about keeping them safe from predators - four legged and two legged!
I remember once as a kid I got a huge egg one day from my little flock. Just ginormous! And then I dropped it. Two yolks rolled out on the ground. I never got another one.😞
My grandpa told me a whistling woman and a crowing hen will always come to some bad end. When I was a kid I had a hen crow and a few days later something got in the pen and killed her. I became a believer!
Sounds like you’ve covered every possible scenario for the chick’s comfort and well-being if it’s the only one that’s nutso. If I couldn’t move it out of the house, I’d be looking to cull it.