To answer your question, I don’t know.
Your 20 could be plenty. Or , your 20 could just be variations of the same 1 idea. Being functional or aesthetic concepts is irrelevant.
First, ideas are cheap. You have come up with 20. Are you certain that these are the only 20? What if you showed the 20 to others and they gave you input. I’m betting you may come up with more ideas after hearing their input. Have you benchmarked related ideas in other industries?
My point is inspiration for ideas comes from everywhere. Be sure you have exhausted your resources before stopping the ideation process. There is no set correct number.
Also, in reality, the ideation process really never concludes, it just becomes less prominent as the development process continues towards the finish. Then there is the gen 2 version that starts it up again.