The Oz stuff has been signaled from the beginning and seems to be deliberate, more the book than the movie. Earlier seasons had Oz elements as well. There was a great reddit thread three or four weeks ago that did a fantastic analysis and I am failing to find at the moment matching all of the characters and how they tied in.
Edit: Here it is, posted after the second episode.
https://www.reddit.com/r/FargoTV/comments/181i2xo/fargo_s5_and_the_wizard_of_oz_limited_spoilers_s5/