i would try doing it on the side for a while and then quit when you physically cant manage doing both any more. You could use your wages to pay for outsources to help you build a first release e.g. designers, logo etc. In my view we all waste 50% of our day being unproductive so you might as well get paid for that bit. Also it takes a long time for a site to start ranking in search engines etc and getting traffic so that's another reason to build something slowly first.