All good suggestions by everyone.
Are you already smelling them at 3 weeks? Are you keeping your coop closed up tightly and how much ventilation does it have? A closed up coop will smell and won't be good for the chicks either - just a though on that.
Slick floors can be dangerous for you and chickens, so be careful in there! A nice thick layer of bedding will help. Once your chicks start roosting watch where they land/jump to and make sure they have deep bedding in that part or they will be skidding around.
Wonder how I know this
Just my 2¢