I concur with most of what is being said here - in my opinion, the only way to make it as a full time author, unless you're writing in a niche genre, is to go traditional publishing. Even if you don't care about getting your story in print, the big thing that a publisher does for you is helps you advertise your story - they get it into bookstores, they get covers made, audiobooks, etc.
They also make a contract with you where you get money beforehand for your story in addition to the money the book will make. Of course, this is a difficult position to get into, but I think if you're putting forth all the effort to make writing your career, this is a far more viable option than tossing your work into the winds of Amazon.