To answer your question, it'll be something like this: "... I said, but I wouldn't." Then, the next person says, "Sure, but why?" It'll be best to use a comma unless you're trying to demonstrate that the person speaking is drawling out a specific word. Only use ellipses when your speaker is drawling a certain word.
Version 3 is the only consistent choice, except that the last item should have a period instead of a comma after the equation, and the "see" sentence should start with cap S and end with a period. Mathematical expressions do take a period according to The Chicago Manual of Style 12.18, which is academic style.