It seems to me that lots of typefaces are at least initially created in a single weight. It depends on the purpose you intend to put it to what variants you would need.

Just a roman is enough for me. But just wanted to make sure that it wasn't necessary or strange not to have one. Kinda felt obligated.

If your goal is to produce a fully featured text face, sure, you need at least a plain (Roman), bold, italic, and bold italic. Small caps, old style figures, and extended ligature and swash sets in each of those styles are highly desirable.

Other than that, making a single style is not at all unheard of.