You don't need to set up an LLC, but it would protect your personal assets from liability, which is something a DBA (fictitious business name) won't do.
Make sure you choose a viable and available trademark to do business under, and make sure you have a good contract to use for your customers. That's where you need a business/IP's lawyer's help.
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LLC would give you come asset ptotection if set up correctly and you can elect Sub-S election for tax purposes.
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