For hives on new foundation, I have done the seven of ten rule. When seven frames are drawn out add another box. If you are using new foundation only add one box at a time or they will make a mess out of things. If you have drawn foundation you can add another box anytime. The hive will grow faster because the queen can lay at maximum rate.
I prefer plastic queen excluders because the sizing of the slots seems to be more accurate. They are lighter and easier to store. If they get gummed up with propolis you can freeze them give them a little twist and they clean up. Here in Michigan I just wait for winter, to clean them up. And oh yes they are cheaper.
The Busy Bee teaches two lessons: One is not to be idle and the other is not to get stung.