An LLC would be best because it requires fewer formalities than a corporation
. Depending on what your accountant advises, you would either file taxes as a sole proprietorship would or you can elect S status and be treated the same as an S-corp for tax purposes.
Forming the LLC is relatively easy. You must file two forms, the Articles of Organization (LLC-1) and the Certificate of Information (LLC-12). Those forms (with instructions) can be found here
You also need to apply for an FEIN from the IRS for the business. You will need this to file taxes and to open a bank account.
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