Take it from me. I've wasted more money then IDE like to admit on how to not do it.
Websites are neat. They are a brilliant way to create a presence on the internet. Now if your trying to build a company. or have little to nothing invested in the real world other then a cool place you want to create. Take it from me.
BUILD THE SITE FIRST, Before you buy the domain.
This however is exempt from physical brick stores. that have a real world existence and need a site.
But many times I find myself on go daddy hunting down a good name. And By god I find some amazing ones. But then it comes time to make the site and either the modification or the idea has sailed off.
Most times you buy a domain for a year. so that means you have a timescale in when you can get a site up. And usually if your site isn't off to the races in popularity its just another yearly expense.
So Build your site and make it amazing! Make sure it does what you want it to do. If you have another domain build it on a sub domain! Get that sucker 100% functional before you invest any time sharing it or investing marketing on it.