What is the minimum useful batch size for making masa harina tortillas?

One cup of masa harina produces about 8-10 standard-size corn tortillas. For two people eating tacos that is the right amount — 4-5 tortillas each for a normal meal. The process for 1 cup of masa takes about 20-25 minutes including mixing, pressing, and cooking. It is worth it at that scale. Below that (half cup), the effort-to-result ratio feels high. Stick with 1 cup minimum; scale up if you want extras to store.

One cup once you have the rhythm takes less than 20 minutes. The first time you make it will take 35-40 minutes because you are learning the dough feel. By the fifth time it is a reflexive process. The investment in learning is front-loaded; the payoff is ongoing.