I ordered mine from Purely Poultry and they all arrived very healthy little chicks and a rooster :)
If I were going to do it all over again I would order from these folks as they were absolutely great to work with.
I think you just need to go off your instinct here. My chicks are a week old and I moved them from their Rubber Maid tub to their coop already, slowly getting them ready for the upcoming winter. I have their heat light on in the coop, but also open the door in the day (with the light still on)...
Mine love a couple drops of apple cider vinegar in their water and they are only a week and a half old. Problem with it is, they poop 10x more than usual but they are happy little things.