There a lot in this that I didn't know, like his first name was Jackson. Something he didn't know himself until he joined the Army. His wife was a few years older than him, they didn't have any children. He opted to be cremated mostly to avoid people writing "he's dead Jim" (a phrase he hated) on his tombstone.
The ring that he wore on his little finger was his mother's. A diamond ring that her brother had won in a card game. Something he refused to remove for the role of McCoy, even though Roddenberry insisted that the characters wear no jewelry.
It was his idea for McCoy to have a daughter (D.C. Fontanna suggested a son at first) since most of his friends were female. The character of Joanna was never incorporated into an episode, however she's "unofficially official" since D.C. Fontanna said she exists in the Trek universe. She's been mentioned a few times in the novels though.
He also had a hard time shaking the McCoy role. other that McCoy i've only seen him in an episode of Ironside playing a pushy jewelry salesman & in a documentary talking about his work making training films during WW2. Pre McCoy he was in a number of Westerns.
The author hinted that the dream that he told his friend about as he was dying was something he made up to comfort the friend. I still like to think it was a true dream.