I’m pretty sure everyone knew before me but the bestest trick for making consistent button holes? A corn cob poke. Since I’ve been making all sorts of buttons, I grabbed a package of them at the dollar store. This poke has the wires squeezed a little more closely (used pliers for that). I have one where the wires are opened a bit more apart.
Lisa of Polka Dot Cottage also explained how she made a template to do this stuff.