You won't have much luck adding younger and older birds together. There will be squabbles, some may be lethal. If a bird bleeds enough for the flock to notice the others will kill it IMMEDIATELY, so be aware of wounds among your flock. Experienced breeders can swap birds around a little but i caution against it until you understand the social structure and the way it operates among these birds.
Roosters can be thrown together in large groups as long as no hens are present or can be seen. I put roosters on the opposite side of my yard in a bachelor cage (waiting room for the skillet). Sometimes I have 30 or more roosters in the same cage.
It reaches 100 degrees where I live often during the summer. My quail have shade but that is there only protection from the heat. Younger birds are much more affected by the heat. When it comes to hatchlings they are really easy to cook with a heat lamp so I recommend having a dimmer on your brooder lamp.