Question on entering maiden names. Do we enter only the last name? Is the first name to be entered as well?
That's correct to enter only the last name. The first name is not to be entered as well.
A maiden name = a woman's surname before marriage.
In your project, that field is titled "Mother's Maiden Name" and you would enter only her maiden name there and not her married surname. If her maiden name was not recorded, you would blank that field.
The article below (and the answer above) give the standard directions for entering a maiden name before the married surname in the same field. But the Project Instructions and Field Helps are what we look at first and for US, Wisconsin—Pre-1907 Death Records, 1860–1907, we are not indexing 2 surnames for the mother, just the maiden name.
When a woman's maiden is name is shown on a record, it is entered on the surname line before the married name. Example--Jones Brown. Sometimes, only the maiden name is shown with the first name as follows: Mary Jones so Jones would be indexed on the surname line.