I feel like a lot of people (not holman) are looking for permission, as if having an LLC is a marker that says "I am a serious business doing serious business things." You don't need permission. You can just do things.

A formal business structure is good (but not required!) if you have employees and/or business partners, or if your attorney tells you you need one. IME as a solo entrepreneur an LLC (or two, in my case) just invited more paperwork into my life.

You know what actually functionally limits liability as a solo business? Good contracts backed up with business insurance.