I'm by no means an export modder, but from the questions I see posted on this forum I noticed a lot want to edit stuff but they don't know that if you make a main campaign mod the game loads everything from the main module (files are linked to the original path), but those files can be overwritten by your own files with correct path naming and redirecting.
Personally I would start with editing visual stuff. Most people want to start there. Changing the way their Hero looks like for example, adding and removing objects, main campaign terrain editing (not so long ago this question popped up), adding a level etc. from there on story scripting and and charscripts maybe.
