Critter-3 is correct, none of that is taxable, if every item is sold for less than you paid for it. It's the online equivalent of a garage sale. It is not a free lance business subject to self employment tax. You do not need to have receipts.
If you sell any specific item, for more than you paid for it, that is technically reportable. But the gain (profit) is taxed at long term capital gains rates.
The Government rules on expanded 1099-K reporting are new this year. We don't know what the IRS is going to do with them (they will be overwhelmed).
But the bottom line, for now, is: there is no specific place on the tax forms to account for a 1099-K. For a detailed discussion, see this other thread here, in the forum. https://ttlc.intuit.com/community/taxes/discussion/i-sold-some-personal-items-on-ebay-and-received-a...
