Get your taxes done using TurboTax

Yes, enter your cost in inventory. Regarding the items that you don't have receipts for, you could use, canceled checks reflecting proof of payment, account statements, credit card receipts, and statements, invoices.  

For the fees that eBay added to your gross amount, I would suggest you report it under Other Miscellaneous Expenses.  To get back to your Schedule C:

1. Open or continue your return
2. Locate the Schedule C section
3. Go to Schedule C
4. Under the business you need to review, go to Review
5. Change your Work description if needed
6. Once make the change, continue the interview until you get to the expense categories (see the image below)
7. Select Inventory the program will guide you as you enter the information

See the images below for your reference: