A good rule of thumb that i tell people looking to go full time i this...

Take what you earn now at your full time job, and add another 30% to that a month.

Once you are making that much consistently for 3-6 months, go full time in the industry.

Things change so damned much from month to month in the biz its always good to make more than you do at your full-time job for a few months and put some of that money aside for when slow periods happen.

Regards,

Lee