Hi! I just saw your introduction thread a little ago!
My husband and I initially thought we'd just have one kid, but kind of keep our options open from there. And our first was a really high needs baby and we thought she would indeed be an only for a long time. It took us 6 years to feel interested in having another, and that one was born 7 years after the first.
My advice would be to take the babies one at a time. You don't have to decide how many right from the start - particularly between 2 and 3. Having an only child might require a bit more discussion. Have you and your husband discussed this? Are you pretty much on the same page or are you feeling differently about it?
I agree that you don't necessarily have to decide right now. DH and I have changed our minds a lot. Originally, I wanted two kids, and he wanted four. We're about to have our eighth! Sometimes he talked me into it, sometimes I convinced him.
Your idea of the right family size for you may change once you're in the thick of it - and then it might change again!
Good advice above. Take it is one child at a time. Your feeling will likely change as time passes and your already present children age. I will say, I was an only and know that having an only child is harder in some ways than having two or more. Easier in other ways, of course, too.