You could have just a large cardboard box for the first few day's/week inside getting them all eating and drinking and, on their feet, then move them to coop if you feel better with that option. But I wouldn't try to brood them in anything else after that with that many and having that new coop...
That 13 is low, some heat plates are recommended for 50 or above. Momma heat pad would work you would need two for that many. I use heat lamps but as stated they have to be secured and used correctly. It would be easy to brood in coop especially since there is no adult birds to deal with.