Fishman65
That is a long time to carry birds for the freezer. I wish I would have kept better records but I had freedom rangers last year that were carried to 12 weeks. I can tell you that they were mighty expensive compared to the Cornish x. If memory servers me I was putting almost 100 lbs of food a week into 37 birds. These dressed at about 8 lbs.
IMO you would be better suited to go with the Cornish X and shorten down to an 8 week grow out. You will end up with more meat in the freezer. This will leave a little more in the wallet too. I have had some heavy breed roos that I butchered at 5 to 6 mos old and there is not
much meat there- I use them for a pot of noodle soup most of the time. I try to avoid this now and buy layer peeps that can be color sexed.
As far as your original post, you would probably need 100lbs to get you to about 3 weeks old ( depending on waste). Then a few weeks at 50lbs and after 8 weeks I am going to say 100 to 150 a week. If you let the range around it may help reduce the feed bill but they will be lucky to make 5 lbs a 20 weeks. Just a ton of variables on the mix. The cold weather turns my layers into eating machines 40 hens will use about 75lbs a week.
Hope the above helps.