You would not need to pay self-employment tax on the money if it was a hobby. It would just be extra income and treated like any other income. You say the book sales is a hobby. If you choose to claim the editing as a hobby, you should be able to use the same Free Edition of TurboTax. If you want to claim it as self-employment, then you would need to purchase the edition of TurboTax that supports Schedule C. There is a chart showing which program covers which tax situations on the main TurboTax page.
