If you don't mind I'll answer this. I'm not sure if Agama reads these boards at all, and she definitely does not post frequently here.

1. You can make keys/door switches using trigger zones and trigger crates. See this tutorial.
2. Frequently occuring "events" are either done using generators for existing events, or animations for tiles.
3. You cannot import ambient sounds. Here's a list of currently existing ambient sounds.

It is not possible to make your own new events as in new things in the game that weren't there before. You can only create tilesets and work with what jcs has to offer you. There's no functionality to extend jcs right now.