Here is a link to the US Copyright Office. They will answer questions regarding copyright for free. I don't think any of the various "Creative Commons" licenses are any substitute for the real Copyright Office.

https://www.copyright.gov/

The problem with publishing on Steemit is that after a month or so, you can't delete or edit your work. As a professional writer this is distressing. Yes I like getting paid here on Steemit, but few if any publishers are going to pay you for your work if it's available for free on Steemit.

The developers should incorporate a way of making your posts inaccessible some time after payout has passed. Otherwise you are essentially losing control of your artistic creation.