So I know not very much about the data editor: why is it that when I create a new actor, behaviour, effect, or ability, there doesn't seem to be any of the same fields and tabs of information that existing actors etc. have? There only seems to be fields for editor information and UI stuff. Without duplicating anything, how can I get more fields to show up?

What do you need to show up? A lot of things show up once you start attaching models to actors and actors to units. The same goes for effects to abilities.

How do I attach things then? Probably what I should have asked first.

What are you trying to attach?

Try pressing the orange buttons on the top.
Seems like that you hided the default values.