FFVI: Divergent Paths

I can't get the patched game to run past the introduction, because the initial Narche battle displays garbled text and then causes the game to crash. What am I doing wrong?

That's going to be a header issue, or rather lack of one in this case:
The patch needs to be applied to a FF3us v1.0 (Headered) ROM. Without needing to know what a "header" even is, you can add one by using a utility such as SNEStuff:
https://www.romhacking.net/utilities/841/

Basically some patches require this, some require it to be "headerless", meaning without, and some patch authors include a patch for both. Anyways, with SNEStuff you'd just choose to Add or Remove Header (using a clean FF3 ROM), and then apply the Divergent Paths .ips patch afterword.