An LLC doesn’t restrict the number of members, and most states allow for single-member LLCs. But whether comprised of a single member or multiple members, the LLC must operate under a business name, not an individual's name, and states generally require “Limited Liability Company” or “LLC” to be included in the registered name (e.g., “Fancy Flower Shop, LLC”). Operating as the sole member of an LLC is not the same as operating as a sole proprietor but does bear some similarities.
As an LLC, you can operate as self-employed and not pay corporate sales tax but pay self-employment tax instead. Or you may choose to be taxed as a corporation. In either case, an LLC protects your personal assets and reputation from your company’s liabilities and debts, which is not the case when operating as a sole proprietor.
Unlike sole proprietorships, LLCs typically need to register with the state of formation. If you intend to operate in other states (i.e., “foreign” states) as well, you must qualify to do business as a foreign LLC in those states. This generally entails obtaining a Certificate of Status (aka, Certificate of Good Standing) from your home state so you can obtain a Certificate of Authority (aka, Application for Authority, or Foreign LLC Registration) in the other state. You’ll also need to pay associated LLC filing and reporting fees. For an idea of what that can cost, check out the New York Department of State’s page on foreign (non-New York) LLCs.
Business license requirements, again, come down to location and business activities.
Before deciding which form of business you’ll operate, do your research to discover the distinctive requirements and regulations for each. You may find one is more appropriate for you than the other. Once you’ve decided your business type, research state and local governments’ business license requirements. Every state, county, and city is unique. Depending on your business activity, you may also need a federal license.