well they can go as close as 12" seems like 18" is a common spacing for higher end lumber. my main point is to keep stickers close to the ends of the lumber and keep the stickers over the one below it. And yes it takes a lot of stickers, it seems like at somewhere I and others mentioned that its really the first thing one with a mill needs to saw out, as well as blocking for stacking. And whatever you do, make sure you use a good butt end or a second cut log for making the sticks, knot free as possible, you'll see what knots do when drying if you have them, let them air out. Keeping these straight is equally as important, they are what your lumber will be sitting on.