If you are raising birds for whole bird oven roasts, I'd suggest processing around 5-6 weeks. At that age, the thickness of the meat on the breast, back, legs, thighs, etc. is close enough that you're not going to have way over-cooked back and not quite cooked breast meat, for example. As the chicken gets bigger, oven roast takes way longer to cook the breast than, say the legs. And it's a lot harder to keep it moist while oven roasting a CX the size of a small turkey. 10 week CX can be MASSIVE, depending on how you feed them and manage them. Anything over 6 weeks, I skinned and parted out, and threw two breasts in a gallon ziplock freezer bag, and two thighs with legs and wings into a ziplock freezer bag. Each bag was one meal for a family of 5 The carcass got its own freezer bag for soup stock later. I like to put whole oven roasts into large shrink wrap bags. Even 10 wk old CX should fit, if you buy the right size bag. Think small or medium turkey.
I had the same questions as you - do I have to chill after scalding? More seasoned folks than I said no, just get the guts out as quickly as possible so the whole bird can cool down as quickly as possible. So I rinse after scalding to make it so I can touch the bird without burning myself, and then work as quickly as I can.
The key when processing, is to do it quickly as possible, and get them into the fridge or into a cooler with icewater ASAP. I rinse with cold water as I go, and if I plan to part out a bird in hot weather, I throw it into the ice bath as soon as I can as a whole bird sans guts. I add all the birds I plan to process to the ice bath. Then once they're all fridge temperature internally, I can part them out in a cool location, inside if it's really hot. Generally rigor mortis doesn't get in the way, but you can also part them after rigor mortis passes.
I rest my whole birds sans guts in a large metal bowl under some plastic wrap in the fridge until rigor passes. I have metal bowls larger than stew pots.
When you put birds in the fridge or freezer, if they're not totally fridge temperatures throughout their muscles, you have to lay them out individually so they can cool off ASAP. Don't stack hot chicken up in the fridge or freezer - it prevents them from cooling off ASAP and can lead to a lot of bad chicken and/or possible food poisoning. An inch flat of chicken cools quickly enough, or one layer of chicken parted out.
I've kept processed chicken in the fridge for 7-10 days without issue, but I'd say 7 days to be on the safe side. I usually process in March, where it is 50-60F outside, in mild sunny weather. No flies. Processing takes me 2 hrs from live bird to whole carcass in the ice water bath if I scald and pluck, and 1.5 hrs if I skin them. If I part them out, it may take another half an hour. In hotter weather, I don't part them out until after they're fully chilled to fridge temperatures, or until rigor has passed. Other folks can process a lot faster than me.
For your first batch of CX, I'd suggest doing around 10-15 birds or less. This will allow you to get an idea of how they behave, how to scale your process, how to deal with poop, etc., and so you're not overwhelmed when/if things go wrong. I'd also start processing them at 5 weeks, a couple a week (hens mature slower), and see how you like the flavor, size of the bird, ease of processing, etc. at each age.
I found that 4 sq ft per bird or more was good for my 150 sq ft stationary covered run for 23 CX. I was out there at least once a day turning the poop into the deep litter. CX don't get out of the way, you have to physically move them so you can put down feeders, or enter coops, or they will get squished. I was gently but firmly pushing mine around with a gravel rake whenever I wanted to go anywhere. I set up food and water on opposite sides of the run so they would walk back and forth - otherwise they wouldn't get any exercise. I put gutter feeders up on cinderblocks so they had to stand and eat. Given the choice they would lie down by the feeder and eat all day. Since you're raising in a tractor, that will be good for them, all that grass, but do expect challenges when moving the tractor. Eggers will walk away from the wall of the tractor moving their way - CX won't. So go slow and figure out a way not to trap or squish feet. Also, make sure from day one everyone has enough space at the feeder at all times. They will cut each other's rear ends open trying to get to the food if there is not enough space. And make sure they don't get wet, or lie in the wet - they are super susceptible to respiratory diseases brought on by getting chilled. They can easily get hypothermia. I keep a hair dryer and some towels handy just in case, and some collapsible dog crates available whenever I have chickens, in case I have another random cloud-burst flood.
I had a 9 week female that tripped stepping off of a 2" high cinderblock, fell over on her back, and couldn't flip back over. She'd probably have had a heart attack if I hadn't seen it and rescued her.
And make sure your processing help will actually help... My husband said he'd help process our very first batch of 25 CX, and guess who did them all? Me. The one who never even went hunting. Has he processed or helped process even one chicken? In 4 years? Nope. The cuteness factor got him, and that was the end of it.
