The earlier responses are spot on about the financial cushion being critical, but I think they're slightly underselling the client-first angle. You don't need to quit and then figure out income - that's backwards. The real move is to spend the next 2-3 months treating freelancing like a side project while you're still employed. Test those interested clients, see which ones actually convert to paid work, figure out what your real hourly rate needs to be to replace your salary, and build some actual repeatable work. A lot of people have "interested clients" who vanish the moment there's a real contract and payment terms involved. Getting 2-3 locked-in retainer clients before you hand in your notice isn't just safer, it's the difference between freelancing and unemployment.
Once you've got some real income flowing and you know what your actual workload looks like, the savings question becomes way clearer. If you've got one solid client paying you X per month, you need maybe 3-4 months of expenses saved as backup, not 6. If it's still scattered, you need way more. The sequencing matters because going freelance with no buffer and no clients is how people panic and take the first garbage project that comes along. But going freelance with even one client paying consistently? That's a completely different headspace.
One thing the earlier answers didn't mention: talk to an accountant or tax person before you jump. Self-employment taxes, quarterly payments, health insurance - that stuff eats into your actual take-home way more than salaried people realize. Factor that into what you actually need to earn.