Hi,
There's a bit of each. You'll certainly want to read the
Overview and do the
Quick Start tutorial to familiarize yourself with the Dialogue System in general.
Then read about
Dialogue UIs and/or watch the
Dialogue UI tutorial.
You may want to bookmark the
Scripting section.
As for examples, source code is included with everything, including the Textline addon and Subsurface Similar example. The comments in the source code should help point you in the right direction.
If you start with Textline, I can think of two approaches. I'll admit that I haven't thought these ideas out thoroughly, so I don't know which one is preferable, or if there's a better different option.
1. You could modify the TextlineDialogueUI script's AddMessage() method to also set additional audiovisual UI elements.
2. Or you could leave TextlineDialogueUI untouched. Instead, define a subclass of StandardUISubtitlePanel that contains additional UI elements. Override its ShowSubtitle() method to also set these additional UI elements, possibly pulling them from custom tags in the subtitle's text. Then use this subclass instead of StandardUISubtitlePanel in your dialogue UI.