Congrats on the new peeps! Looks like your coop is going to be beautiful! You are most certainly on the right track to raising a very happy and healthy flock. Using a hardware cloth divider for introducing new chicks is a great idea, I have used it several times with success. When figuring out when to introduce pay more attention to the size of the chicks then to age. Bigger ones are always going to pick on smaller ones, just a part of chicken nature. But keeping them close in size will help keep that to a minimum. Good Luck and Enjoy!