I tried this a few years back and I almost went broke! The thing is, I started with no savings, I was banking on income coming in quick and it was a disaster the first 6 months. Now I've got a decent emergency fund and things work way better, but that's only because I went back to work while building the business on the side.
The harsh reality is most online businesses need time to take off, and without cash in the bank you end up stressed, making bad decisions or worse, getting into debt. If you really wanna do it man, get yourself that cushion first - even just a few months of expenses saved up - and keep your job while you figure out if the business actually works!