I agree with you in 100%. "Don't be afraid to give up the good to go for the great." John D. Rockefeller
You should leave your job only when your online business income can replace the income you receive from work and you have a back up.
well first I would try to push the site forward to see how much potential it has and keep the job. Then if you see you are sucessfull and also might want to start another site, just try to work parttime (if this is possible in your area) and then if it shows off everything is working fine and you have some sites making money constant quit your job (if the money is as much as you can earn in your job) This is how I would try my luck
Every business eventually has to slow down to speed bumps. I wouldn't quit your day job until you have at least enough saved up for a year or two in case of rainy days. Try to find ways to let your money work for you instead of you working for money. If you register your business, you maybe able to hire interns to work for you instead. Working as a one man army can be pretty stressful.
This is a very delicate issue and the solution lays on you. There are some things you need to reconsider, for how long have your site been generating sales for you on 2 to 3 days. If its up to six months then that would be great. Then the other aspect which you have answered yourself. You are ok with what you are currently making. Then do away with the goddamn job and experience the job of working for yourself.