It is not necessary to be an LLC, you can be only a sole proprietor. However, the protection of an LLC means that should you be sued, your home, vehicles, and personal property are protected from seizure.
I cannot advise what to do, but we've opted for SP to start with, and in a year revisit the LLC option. Setting up an LLC costs around $300-$500 (we're in California). To us, it was worth it to wait a year. It really depends what you have, financially, to put into the business; had I had the excess funds available I would've gone for it out of the gate.
Hope that helps.