Hello and yes starting a new business in a huge endeavor and it comes with more responsibility. As you mention becoming an LLC would not have any huge financial impact if you are single-member. The election of becoming an LLC is normally at the state level. For federal purposes, you will need to figure out which classification best suits your business
https://www.irs.gov/businesses/small-businesses-self-employed/limited-liability-company-llc
With regards to sales tax, this can be very complex if you sell across different states. If you only sell in TN, it may be a little less complex but I would definitely check out https://www.tn.gov/revenue/taxes/sales-and-use-tax.html
I always recommend using a software that suits your needs as doing this the old fashion way (pen and paper) never yields the most favorable outcome.
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