My main goal is to be able to constantly keep track of individual text fragment word and character counts while simultaneously being able to read the entire long document as a whole.
As I discussed on Root Access, the broad class of tool you're looking at is an outline text editor. Outline editors let you work in blocks of texts, treat them as discrete units, and link them together, perfect for your use case.
As far as ANYONE I have talked to who needs/has used one has told me, literature and latte's scrivener is the program to beat, though this answer on Ask Ubuntu suggests a few alternatives.
If you're willing to consider a bit more than plain-text, then this is very possible. Two such ways are using Markdown (which doesn't have native include support, but several document processors do) or LaTeX.
With minimal markup, the Pandoc route may be what you want, since your text fragments just need to be written as Markdown documents (which, without using any additional features, are still just plain-text documents; this is the formatting system used here on Super User and the other Stack Exchange websites). Inspired by this SO question, let's say the text fragments are in the current working directory:
These can be merged & rendered as a single file with Pandoc using the command:
Pandoc is also compatible with the LaTeX format which may also serve your needs, although there are indeed several other LaTeX document editors/compilers which might be better suited to the task.
Consider creating a rather simple LaTeX document, and place your plain-text files into several other files. You can then use the LaTeX
So, you might want to create a parent .tex document to wrap all of your sub-.tex files (which just contain plain-text; LaTeX's
You can then make another file to compile (e.g.
You can then compile the