Honestly the jg and beams are slow growing in my opinion. They do get big but it takes 4-5 months don't lay till 6 months. The Ross are ready at 10-14 weeks . Start laying at 3-4 months
Man that's a lot of space you could put 50-100 chickens in there depending on breed. 5-10sq ft a bird for run 1-2 for coop. With that space I could have some fun and i have 34 birds