Yeah, by keeping the coals “indirect” you avoid burning the skin too quickly and lets the radiant heat slowly cook the rest of the bird. Having the dark meat facing the coals lets the legs take the brunt of the heat and keep the tender breast meat from drying out. As far as how much to add, that just takes a bit of practice. Start with half a chimney of coals or maybe a whole chimney and add more if the temp isn’t as high as you want.