Personally I read to make sure I used no animal protein- broiler feed has feathers and ground up birds etc. Yuck.
I began our birds on medicated starter, changed to unmedicated crumbles, then to layer feed (it was cheap $5 for the 50 lb bag) then I went to a fat and finish- mind you we only had 6 birds.
They did not stay up at night, placed them in a shady area in the yard for coolness, the only time they had a heat lamp was for the first week, after that it was warm enough to let them go without the light.
At 8 weeks they were still able to get up and move, even tho they sat each time they moved! All weight approx 6 ish pounds each.
Good luck to you! This year I am planning on building a wire ground level pen to move each day, that way the can enjoy grass.
Good luck with your choices!