You file only one Schedule C with all of your MS income declared on it. AND that includes MS income from MSCs that do not have to provide you with a 1099 because you earned less than the amount that triggers a requirement for them to send you one. Therefore, you must be sure to record all of your fee income (and your expenses, of course) in order to file taxes. The first year, if you owe Self-employment tax when you file, there would be no penalty because there was no filing history for that business. In subsequent years there could be a penalty for not paying enough in quarterly taxes, including SE tax to meet one the the IRS's three or four tests of "enough." Those tests/criteria are quite straightforward, but I do not have access to the instructions at the moment.
I have been self-employed all but 3 years in the past 50+ years and, yes, I have had a small penalty at times that was clearly due to underpayment of SE taxes, since, in some lean years, those were the only taxes that I owed, lol.
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