A flare takes exactly one craft of gun powder. That makes it the tidiest order on the bench: any number uses the batches to the last grain, and the calculator never shows a leftover. The cost to think about is what that batch could have been instead. It is the powder of two buckshot shells, and early in a wipe the shells usually matter more.
The blueprint is among the cheapest at a Level 1 workbench, so learning it early hurts nobody. Crafting a stack early does. Wait until the furnaces run through the night, then keep a full stack by the window you defend from.
Watch out
Crafted flares are not banked powder. The recycler gives back only about half the gun powder and metal fragments, so craft them for a night, not for storage.
