You can't actually solve a lot of problems by throwing money at them. Ensuring that scaling your core application to arbitrary traffic sizes is in the class of money-solvable problems isn't trivial and should guide your architectural decisions from day 1.

Yes, you'll probably end up doing significant rewrites if you do actually win the lottery and get big, but it's nice to know that you're not going to top out at some arbitrary size and have to start turning customers away while you do those rewrites.