Dreams of a Doubtful Writer

I am asking myself the hard question, "How do I plan to jump start my writing career?" And to be honest, I don't have a writing career, yet. I'm still a struggling writer that no one has heard of except friends, family, and classmates. I don't even know if I have enough credentials to call myself a writer, but I am one (I've been one ever since I was in elementary school). I dream of penning a book that becomes a best-seller. I want to earn tons of money and travel the world promoting my book. I want to be interviewed by the best journalists and have my photograph donning the front cover of Poets & Writers. At least, that is what I want, but will it happen? Right now, I'd be satisfied with having one of my works be published in a major literary magazine, but I don't know if this is achievable. Right now, I know that I need to write more, but I feel blocked. Like the blank page is a challenge. A test. And I don't want to fail. To put it bluntly, I'm a very practical person, and sometimes the idea of being a fiction writer seems too lofty. To write a well-written piece of work takes a lot of time and effort. And in spite of your hard work, there are no guarantees, and it is this realization that is preventing me to write. For example, I really want to turn in a manuscript to The New Yorker, but there is a huge part of me that feels it is a waste of my time, but we never know unless we try, right?