Can a new writer make enough money from book sales to become a full-time writer and stop working?

Eventually, perhaps. It takes time—years—to become a good writer, to establish a readership, and to cultivate your craft. But you won’t “stop working”—you’ll simply change jobs. Writing is hard work, and you’ll spend hundreds, if not thousands, of hours in your writing chair. I’ve been writing 41 years, so I estimate that I’ve spent 60,000 hours writing at my desk. :-)