There are some divergent themes here. You can free range cornish x's but don't expect them to be ready to process in 8 weeks. Feeding the 12on-12off method will allow them to get big enough for slaughter in 8 weeks. The chicken tractor is a compromise between the two. These buggers are like no other chicken in the backyard flock. I think they should be an entirely different species, myself. So you need to decide what's more important to you...Quick turnaround time or free ranged meaties. Actually, if you want free ranged meaties, I'd go for the freedom (colored) rangers. They take longer but will forage for a higher portion of their diet.
I second the water consumption....They drink LOTS! They eat LOTS!....and they poop even more than they eat and drink! Poop is the reason why you want to move them at least once a day, if not more. It's easy to move the chicken tractor if it's got wheels. This way they get a fresh patch of grass to eat supplementing the store bought food.
At 8 weeks, my Cornish X's struggle to hop over the 2x4 cross members of the tractor. These members are in contact with the ground so you can imagine how obese these guys are if they struggle to keep their balance when they go over the 2x4. during the day, some of mine will sit on top of the 2x4's but at night, they just huddle up on the ground under the covered portion of the tractor. That's the other reason to keep moving the tractor. It's won't take long at all with 50 birds to cover every last bit of ground with poop. They lay down so much that they end up laying in their own poop. By moving, you're getting them off their poop and onto clean ground...temporarily, anyways.
A great benefit of this is the grass will really grow like mad next year! We started raising Cornish x's last year and we didn't have very much grass at all. The previous owners of our house sold in the middle of landscaping and we had bare dirt. Not even topsoil, just dirt. Every place the tractor was last year is thriving and we have multiple varieties of grass that are about 2'tall now. (I need to trim it) Everywhere we didn't have the tractor is the same dirt. It's night and day. Once I get coverage over all the bare dirt, I'll be moving the tractor over the tall grass and let them tear into it.
Dan