I fed the medicated till I ran out (50lb bag). We were feeding between 10-20 birds so maybe the first 3-4 weeks? My daughter had the records (had to keep track for 4-h) but we'd switch over when we ran out. I probably won't use the show chow for this new batch--kind of experimenting as I don't want them as huge as they were for the fair. We couldn't process the ones that DD didn't take until a week later (9 weeks) and they were huge! Would like to process at 7-8 weeks this time. Still waiting to hear back from processor on a date.
They ended up weighing about 9-11 lbs on average when they went to the fair, after processing about 7-8 lbs.
These were the "leftovers" that didn't make it to the fair in 2014 (2015-no poultry shows in Ohio so she didn't do a project her last year in 4-H).
I would make sure you keep food and water at opposite ends to make sure they move around a bit--they'd be content never moving the last couple of weeks--eat-drink-poop in one place.
As far as mixing with layers--personally I wouldn't. they are totally different creatures--slower the last few weeks, waddling around, getting jumpy (which worried me as they are prone to heart attacks ). My layers (I have 26 in the big coop) are pretty active and I think they'd pick on them. For the short time we have them I like to keep them content and unbothered if possible. The meaties need a bit of room, but not a whole lot--a tractor would be wonderful, someday we'll make one, but until then I'll keep them safe in a run of sorts. I rig up a pvc fence that's about 8' long and a foot high with wire and block off an area in the coop (outside of the layers section..ends up being about 8' x 5', put shavings down and they are protected and have room to move around. I also keep the food in front of them all the time--I know folks will vow they have to be 12 with, 12 without, or feed set amount twice a day but this has worked for us. I figure they're not eating at night when it's dark and when we would run out during the day they would gorge so frantically, stepping on each other, coughing as they gorged...wasn't worth it.
Good luck weighing them..We had a large screw eye in the doorway of the coop (a 12'x16' shed), then a nylon rope with a hanging luggage scale on it. Used a 5 gallon water bucket for the birds. A two person job--one wrangled chickens, the other (me) wrote down numbers.
Just remember to weigh the bucket first and subtract that or you might shock yourself with the weight. :) I'm sure ours wasn't really accurate as she just needed to have a trio that was evenly matched weight wise and weighing at least 12 lbs total for all three. This year is the first time I've raised them solely for us and a couple of friends. Usually we're struggling with July-Aug. heat concerns..now they're stinking up my mudroom and we're only at week 1.
They won't be outside for another 2-3 weeks...well, maybe out in the coop under heat, but I have 6 layer pullets who are 5 weeks old and still need the heat...they're in the big brooder. Need more!
You may not run into leg issues if you withhold/limit feed. We'd end up with one or two lame birds, once with a "sprung" leg but he could still get around. I just hoped he'd be ok for a few days until the trip to freezer camp--didn't want him to suffer, but he got along ok, just not really graceful.