I do 95% made to order, because I never know what will be popular any given week. It goes in waves. Of course, it's a very personal decision for everyone, many people find it stressful.
I do always have yarn for at least 2-3 items at home.
As a knitter/Crocheter you really should not rely on buying yarn from craft stores, since their prices will eat into your profits. There are great online yarn marketplaces that sell yarn for much friendlier prices. You have to order in bulk, of course, due to shipping costs, but it really pays off. In addition, they also have WAYYY bigger selection of yarns and colors anyway.