I have 25 Colored Rangers in a coop that's 6'x8'. They have a run that's 25'x40'.....but won't go out in the snow! They're terrified of the snow - crazy boys!
Because of the unusual winter conditions, they're NOT interested in hanging out outdoors. Which means bedding costs have tripled for this batch vs. the batches I've grown in the spring/summer/fall. I'm out of room to put composting litter and snow - we'll see what the next round of weather brings us. Ugh.
This batch is now 9wks and what I consider small for their breed. Not sure if the cold is slowing their growth, the lack of extra forage or what's going on - but they're about 3# per bird, not the almost 5#'s their summertime counterparts have been.
I built a PVC tractor that was 10'x10' - and for 25 birds it worked well until this sort of point - where the birds were about 3# to 4#'s each. Then, they simply did not have enough room to turn around in and pecking issues started becoming a problem. I put a 10' piece of plastic gutter for the feeder (cut into a 6' section and a 4' section) which allowed almost all the birds to eat simultaneously - that cut down on fights. But after 4#'s, I ended up using one of their 4' metal feeders also (so a total of 14' of feeders) so everyone could have space at the feeder.
So for your size tractor, I'd recommend getting 25 birds, but culling some at about 3#'s - makes good Cornish hens! Then, you'll have good meals that are worth the effort - and give others room to grow larger for more meat per bird.
Good luck! We've found the meat absolutely wonderful and haven't looked back at buying meat at the market (doesn't matter the market). It's not hard to raise extra birds especially when you factor in the total cost. This batch of Rangers will be (in feed) about $12/bird. Can't beat that price anywhere! However, add in bedding, my time, etc., well, I do it to feed my family REALLY good food. The downside is no one wants to go out to eat anymore, as the food at home is TOO good. So I've asked my teenagers to take over dinner planning/prep/execution on 1 night a week so I get a day 'off'! I do the dishes, but they cook that night.