I made about 100 Christmas cookies, medium size, and I wanted to get an idea of how much royal icing I need to make to decorate them all. I plan to outline, flood, and decorate each one. If anyone could give some insight, it would be greatly appreciated!!! 

From one batch of NFSC recipe, I get about 44 medium cookies. I use Toba's glaze recipe (3 c powdered sugar, 3 T milk, 3T corn syrup, .5t clear vanilla, 15 drops brite white coloring), and that does a base coat of 3 dozen cookies.  I use the glaze as the base color and embellishments with royal.

I would make 2 batches of the glaze, and one batch of royal (4 cups powdered sugar).

BTW, I LOVE using the glaze in a squeeze bottle and using that to "ice" the cookies---- no outline needed!Swirl the tip as you go to push icing just to the edges, go back with a pin/ scribe to prick the little air bubbles.