In the US, you're already a sole proprietorship without any registration. Of course, if you're actually doing business, you probably want the protections of an LLC, which requires registration and fees. But you can accept uncompensated gifts as an individual, and you can accept business income as a sole proprietor, all without registering for anything in particular. You are, as always, required to file accurate taxes, including estimated withholding.
Number of employees or members isn’t relevant. Types of behavior performed is. It is worth talking to a lawyer about this if you have enough revenue this matters.
