Yes, only one action per event. I think it simplifies edition and processing. But note that we can have 2 "touch down" events with 2 different actions.

About appearances, we could still set extra parameters in the event. E.g., time event has a time parameter, so if we needed to set an appearance parameter, we could do it in the event itself. Although to implement old 1.5 actions I'm thinking in a more general approach, in which we define all our actions (examine, grab, talk to...) somewhere in the editor and then you can refer them in the behavior of the scene element.