How can I make Emacs always display the first line of a file which contains header information (such as a CSV) as I scroll down past where it would usually no longer be visible?
Make it a header line.
A window can have a header line at the top. It does not scroll out of the window, but remains displayed at the top. I guess that's what you are asking for.
You could also split the window.
C-u 1 C-x 2