I'm going to page @Mike9241 but, first of all, a single-member LLC (without an election to be treated as a corporation) is disregarded for federal income tax purposes; it is treated as a sole proprietorship.
Also, your P&L from trading, with an MTM (475(f)) election, will not be reported on a Schedule C (which will be used for trading expenses) but will be reported on Form 4797.
You can still have "long-term" accounts.
