For the record, during the first few days before we had to evacuate from the fire, I had all 35 Freedom Rangers in the mini-van coop at night and having access to both the coop and the tractor during the day. Then came the week where they were in the mini-van coop at night but had access to my sister-in-law's garage and dog run during the day. They then spent about a week with a nice lady at her ranch while we cleaned up and got the homestead ready for them after the evacuation. I moved 13 of them into a new grow-out pen that I built and had the two I was planning on keeping in with my layers. We did some repairs to the tractor and added wheels to make moving it easier and then moved the remaining 20 back into the mobile coop/tractor. Two nights later four were killed by that predator break-in, and since then we've reduced the remaining 16 down to 9 (had one for dinner last night and he was delicious).
I think that if we were going to use this setup for adult birds, rather than juveniles, 9 or10 is probably about the right number. The coop seems very roomy, and the run, since we move it every two days seems adequate as well, but if the van needed to be parked for any significant time (like the winter months) it would seem small for more than 9 or 10.
If I do this again next year, I need to do some work on the way the tractor attaches to the trailer hitch. On the original layout, the trailer hitch came right through the end of the tractor and dragged the tractor when it was time to move it. This worked OK for the initial move to the meadow and about 2 moves afterwards, but started tearing the end of the tractor off when we met with uneven ground. Once the wheels were added, it moved much more easily, but the wheels lifted the front of the tractor up enough that it didn't line up with the hitch anymore.
What I've been doing every time I move it is move the van about 12 inches from the tractor, insert the trailer hitch, lower the wheels, insert a thick piece of plastic tubing behind the wheels and fasten the tractor to the hitch with a little piece of rope. I then move the whole thing the length of the tractor to fresh grass, remove the hitch and either back the van or push the tractor forward until they are in contact again. I'm getting pretty good at it, but it isn't as convenient as a proper hitch arrangement. I'll work on it once all the Freedom Rangers have vacated the premises.