Where do numbers start?
The right answer depends on what your context is - this is typical of "truth valued statements" in the context of mathematics.
2 and 3
I've arranged those answers in roughly the order that a person will first encounter them.
If you are learning numbers, you really need to grasp the concepts behind multiples of them before you can understand them.
Let's say you are counting sheep. You need to understand that they are the same thing ("sheep") and you need to understand that you only count the different things that are the same (you can't count the same one twice).
And once you learn to count one thing you then need to understand that you can count other things. And this can give you a different number. Of course, stopping at 3 would interfere with this learning, so there's more to it.
Anyways, once you understand numbers, it's reasonable to talk about having only one of something that you count.
It's even reasonable to talk about not having any of something that you can count.
See what I mean by contextual?