Datarefs fall into different categories
Indicators - (A heading indicator that displays the aircrafts current heading)
actuators - (The knob on an autopilot heading dial that changes the heading bug and commands the aircraft to follow a specific heading)
(Also some are writeable and some are not. Some are ratios...0 to 1... and some are booleans...negative numbers, 0, positive numbers)
And then they can fall into the different types of systems
air driven gyro
electric
AHARS
Whenever you see a "TBM" dataref, it's a custom dataref that is code driven.
a "sim" dataref is a default dataref that comes with X-Plane.
In some cases, the TBM uses default datarefs, because many of those work very well.
To answer your questions,
1. a dataref that is an actuator can absolutely trigger a sequence of events that trigger and activate indicators, and if there is code attached, they can also trigger other actuator datarefs.
2. actuators and indicators, yes. In most cases.
3. 1 triggers the next, and then the next, and so on.
(I hope this answers your question).