I don't know if you've already exhausted the internet on finding blogs of self-publishing authors and getting a real feel on what success looks like and requires as a moneymaking business, but thought I'd share one of my favorites that I got a lot of tips and info from as a marketer for my husband's self-published books:
http://www.lindsayburoker.com/Making decent money as a self-published novelist is possible, but there are some qualities that significantly play into your chances for success. First is your talent as an author of course... good material has a chance of selling, bad stories won't sustain a career. Second is your willingness to take on marketing and promoting your books yourself, and it's mandatory to learn how initially and then keep relearning how as the self-publishing landscape shifts. Third is the intent to write many books to build your backlog, as this both helps the economics of your marketing efforts while also providing more chances for sales as you build fans. Fourth (and this should have come earlier) is your willingness to invest small dollars or gather a cadre of friends to help beta read, edit, do professional looking cover art, start a website, and anything else in the total package you can't handle yourself. Making money as a self-published author is a real job that takes a lot of effort.
There is a ramp-up to building income as a self-published author as well. Even if you want $40K/yr and you have the talent and will work hard to achieve that, I've never read a self-publishing success story where that happened in Year 1.
One other idea, if you want to give yourself a focused project and deadline to see what you can accomplish toward a novel, consider NaNoWriMo:
http://nanowrimo.org/I've never done it but know a few who have. It provides structure that might help kick off your efforts to write.