Current questions and answers regarding the map editor.

How do you add your own music to a map scenario so that it also plays for other people?

If you need background music specifically, then:
in the root folder, there is a folder called music\AdvMapTerrain; put your music there (ogg format). Then, in MapPropertiesTree: go to the music tab, click [...], and you'll see a list: Dirt, Grass, etc. In each of these, the Name field indicates the music that will play in a particular terrain. If you want the music to play all the time, add it to all of them. However, this will affect all other maps.