Is there ONE Scotty Novel I should read that will give me insight into his character?
No, there isn't. I rather wish there was, but most of the novels treat Scotty very inconsistently, characterization-wise and none of them really dive too deep into his backstory. The only two I could venture to say are reasonably done are Kobayashi Maru (47), where he's a puppy cadet, and Vulcan's Glory.
If there were a good, character-driven, well-characterized novel about Mister Scott... I wouldn't have had to write my own.
Good luck on your endeavor!