Word can easily handle a 1000-page document.
What you are describing would be ideal for use of the Master Documents "Feature" if only it worked. (Read the page linked, and maybe links in that page before you even think about using this on anything valuable.) IncludeText fields should do what you want. This works best if the files are based on the same template and use the same Styles for the same purpose.

Again, I'm not sure why this can't be in a single file.