re: Becoming a professional woodworking or not

All very good points and research.Yes Bill sales tax(I forgot that one since there is none in my state) plus registering to collect sales tax,all of a businesses overhead,rent/morgage,utilities and yes insurance plus in some states and counties, contractors licences are required to install what you make,cabinets, and or built-ins and maybe a special certifications for commercial installations,of course contractors need a specific type of insurance .
Adding another area to think about is finishing,as a hobbyist you can wait days and maybe even weeks for your finish to dry but as a pro time is money and having projects sitting around waiting to dry takes up space,so learning about finishes that will dry quickly and that are durable is very important for a more productive operation. Reguarding finishing many governmental agencies will restrict what type of finish you use and how you apply it and perhaps even require a certified spray booth.