I'm in a similar position, but I'm a freelancer, it is much easier to gradually transition from one field to another.
I think you are ready when you have:
- FU fund for some months of comfortable life in case something goes wrong with your new venture
- a very good deal with a publisher and/or enough loyal followers who would buy your art
- at least 50% of your first project complete, I would make it 100% to be sure
Ideally I would not quit, but work on my first project in my free time and then take a vacation + unpaid leave or something for final publishing stage and send a notice only when it's a sure thing but some people have more chances to succeed when there is no way back.
Another important lesson I've learned is you have to make your health one of your highest priorities while you are doing it. Even if it feels like you need to put more time into your work, you should never ever do it at expense of working out and proper recreation in natural environment, this is what makes you productive.