I built a tractor a few years back to keep seven hens and a rooster during part of the summer. Those tractors can get pretty heavy. I built two different sections so I could move it by hand, each section 4’ x 8’ so I had 64 square feet total for 8 chickens. With 8 adult chickens I had to move it every two or three days. If it rained and got the ground wet, two days was stretching it but I did occasionally get 4 days if the weather was really dry. Some people on this forum that have tractors move them a couple of times each day but I think a lot of that is an attempt to keep them from stripping the grass. We all manage them differently.
I'm not sure how you have that henhouse part set up. I'm not sure how you could get four nests and sufficient roosts in that space for your nine chickens when they grow up. If all it is used for is nests or sleeping and they are never locked in there during their waking hours, the actual size of the coop section doesn't really matter. The space of the entire coop/run is what matters. Eight week old birds do not require nearly as much space as adult birds so think ahead.
Is it for nests only and they will use the roosts in the run to sleep? At 8 weeks there is a reasonable chance they are not roosting yet but are still sleeping in a pile somewhere. If they will be sleeping on those roosts in the run, it is possible for something like a raccoon to reach through the holes in the 2x4 wire and eat them by parts. You might want to put some hardware cloth along the ends of the roosts so a raccoon or whatever can't reach in and get them while they are sleeping.
Four nests are more than you will need for 9 hens. Two would have worked. It's probably not worth the effort to remove them but you could possibly have saved a bit of weight, space, and building time by making only two.
I'm not sure what your climate is like. Those tractors are generally best for the better weather. They can present some challenges in winter in many locations. The vegetation may be covered with ice or snow. They may be harder to move. Tractors don't have to be as big as regular fixed coops and runs, but you do need to move them fairly often so that smaller space is not so important. The poop builds up pretty fast too. But if the ground is covered in snow, what good does it do to move them? There is nothing new for them to explore and they may feel confined to the coop part.
What I'm trying to say is that in some climates and in the better parts of the year tractors work great though they are a time commitment since you have to move them often. But in some climates they may not be the best way to overwinter a flock. I have no idea what your conditions are like.
As far as if you are missing something in what you have, chickens need food, water, protection from predators, protection from the elements, and a certain amount of living room. I don’t know enough your set-up to be able to answer your question. Can you keep the food dry and the water not frozen?
When you confine them like we usually do, protection from predators and the elements becomes our responsibility. I’ve seen flocks totally free range and sleep in trees in zero degree Fahrenheit weather. They would go years in between predator attacks. But they had the freedom to choose where they would sleep to get the best protection from predators and especially from the elements. If they are confined they can’t do that.
Living space is a lot harder. There are no magic numbers about how much space a chicken actually needs. It all depends on how we manage them. Commercial operations have techniques where they can keep them in less than 2 square feet total space for each hen. If there are roosters involved in a breeding operation they need more space. One of the techniques with a tractor to get by with less space is to move the tractor often. Exactly how often and whether or not that works for you depends on your unique situation. But if your management techniques and set-up provide food, water, protection, and space, you don’t really need anything else.