Lovely, lovely post Sleepy thank you.
Jessie we're chronic over-thinkers too, especially me. DH believes that it is ultimately my decision, which I appreciate but also find stressful.
I have realized I have been a bit off topic from your OP, as you were asking about having more than one, not about not having any, but if we were to have children I would strongly want to have more than one (though I do realize that I am not in control of that at all). One thing that occurred to me on this point: I was visiting an old friend and her family at Christmas and she asked about our plans re: kids and I mentioned career timing, money (big factors for us), and feeling like I wouldn't want to have only one but was afraid we wouldn't have time for more. And she said "but surely it's better for you to go ahead as soon as you can and have one than to have none at all, right, if you want kids," meaning that she thought we should go for it even if it was likely that we'd only have one. It was a really useful comment for me b/c my reaction was not "oh, gosh, she's right, we should get on with it and just make it work, b/c the main point is we want to have a family, however big/small it may be." Instead I thought "but I really wouldn't like having only one at all, I don't like that picture."
And then I thought, hmm, if I only like the idea of having children if it conforms to a specific picture, then maybe I don't actually like the idea of having children. From what I've seen, people who really want children don't go into it thinking that they only want it if they can first build up x money and achieve x career goals and only then have x many children. Sure, it is perfectly normal to try to build up x money and achieve x career goals and have x children, but if you really want children and you are running out of time, you don't say "ah, but sadly I did not achieve my financial and career goals in time so I just won't have any." You go ahead and have them anyway and just keep working at the other goals. Again this is just what I've seen in my friends, many of whom are now having kids at non-ideal times re: careers and money b/c it's now or never for them too.
Gah this is long. (See, over-thinker!) My point is just that I think stalling on how many you can have may mean that you don't want any and are not comfortable admitting it to yourself. I realize this probably contradicts Sleepy's post, which I did love, and I'm not saying that this is the case for you at all. But since you posted your OP I have realized that anything else I have really wanted, I have gone ahead and done even though I had doubts and it was not an ideal time and I knew it would make things harder. I'm really starting to think that if I wanted children I wouldn't be waffling around like this looking for reasons not to such as being able to have only one. Maybe that will be useful to you to consider, if you just ask yourself, am I waffling b/c I don't want to admit I don't want them? I am really not trying to tell you that's how you feel, just thought it might help you clarify one way or the other.
I'm afraid that again this is a terribly unhelpful post but it took me forever to type so will post anyway in case it is at all useful 