XYZ: in virtually every American state and/or jurisdiction, it would be illegal without at least some license.
lots of people do all the time
each community does require a business license but they don't have inspectors roaming the streets to find businesses that don't have a license
No. You must apply and be issued a license for any business.
Hobby businesses don't need licenses. If you make less than $500 a month you need no license.
Mobile sellers permits are low cost and what you need if you are selling at events, not out of your home. In WI and PA the mobile sellers permit is a one time $15 fee, it automatically renews every year for free.