From my research on the subject of scratch is that there is not much in nutritional value but it keeps them busy. I use it only sparingly, more during the fall/winter rather than the spring/summer. I personally wouldn't put out "scratch" until they get closer to egg laying age. The starter...
Keep in mind that chickens will seek the highest point to roost. Make sure your highest point can accommodate all the chickens or they will fight for a spot.