For instance, my rainbows plugin, parses a string into html with text colors stylized into a spectrum. The actual parsing is complex, but has nothing to do with nodebb. If I had made this functionality into a separate module, I could have easily used it in other projects, while making maintaining the rainbows plugin easier. This is just a small example though, where the separation isn't really needed, just nice to have.
For something like a movie db, there are probably existing modules that can do some of the functionality you want, and I would use them if they exist.
I would be happy to take on such a project. My rates tend to be lower than average, but I am constrained on time at the moment. E-mail the details if you are interested.