On the Mac, it looks like the max file name is 255 characters (including file extension). And when I nest that file inside several folders, I can still place it. When I check the file path, it is 285 characters. Hm!

You might consider posting this as a wish list feature (InDesign should allow long file path names on Windows) here:
https://indesign.uservoice.com

wow, that’s interesting… I don’t think I’ve ever tried it with such long names. The Data Merge feature is really old, and it would not surprise me if it does not work with long names on Windows. (I’m currently running Mac, so I can’t test this for you.)

@Michel: How is this helpful. Yes, we understand that all things are possible with scripting. Are you trying to sell your scripting service? Or are you giving the script away? What is your intention here?

I think what you’re talking about is called “imposition.” InDesign’s book feature does not do imposition.