I understand why you would be concerned about this, but some companies make an excellent business out of having more customers than inventory. A smooth growth can give you something that's profitable from the beginning; even if it's not a huge profit that's not a bad thing. If you really are going into a new market where you have a chance to become the leader by growing fast, you'll probably need to borrow money or get outside capital.
This is a great example of the differences: Strategy Letter I: Ben and Jerry's vs. Amazon - Joel on Software
(not my site, I just re-read it last week and thought it would apply here).
People make mistakes in both directions; some companies set up lots of infrastructure and barely managed to get a few customers, while others (a tiny fraction) have no idea how fast their idea will take off. In the end, the best thing you can do is think through each possible outcome, so once you start you won't be caught by surprise and wonder what to do while you lose money.