One minor thing that frustrates me is that How Long to Beat lists Super Mario 3D World and Bowser's Fury as one entry on the site, whereas I think of them as two distinctly different games. As such, the completion time for both games are mashed together, so you don't get a good sense of how long either one of them are.
I finished the main story last night. It finishes up at 50 Shines and kind of forces you to finish it then. There are a total of 100, some of which open up after you finish the main story.
One thing to know is that when you get to 47 or 48 Shines, Bowser doesn’t go away, so be aware of that. I was getting frustrated with this.
Overall, it actually feels like much more content than I was expecting. The estimate that I heard of getting 100% in 3 or 4 hours is grossly underestimated. It’s a least 10, but probably closer to 15.