" several hundred pages of code"
Wow, you printed it out?
Is it very complex, or do you have lot of similar lines, like some beginner's sketches we can see here, ignoring the usage of arrays, external data files and such data structures?

In Processing too, you can create classes, and can split the code in several files, by creating new tabs.
It vastly depends on what your code looks like.

It's more of a hypothetical question at this point, I'm just trying to figure out the best method for organizing a large project in processing. 

Edit:  Okay, I see what you mean now.  Apparently I only have to drag and drop new files into the project folder and restart processing to be able to use any code from files located in the project's folder.