Hi,
The first line in your brief says "I need a front and back cover design for my newly finished ebook"
So if its a ebook you will be needing the front cover only.

If you have in mind of printing the novel in paperback/ hardcover, then you should also give the exact size, including spine.

The front and back images are for marketing of the ebook, not for print uses. Thanks for the comment though, others will have had the some thought.