Here’s an excellent article about the domains needed for your author platform. Get domains set up well as early as possible. It’s one of your major decisions and needs to be done as early in the process as you can manage.
Get domains set up well!
Your entire marketing effort is built on your domains. That’s the source of your Facebook posts, your tweets, your pins, and so on. They are all ephemeral. Your website/blog is relatively stable and long-term in this crazy digital world.