I agreee that it is more than hard to follow this thread if you did not follow it in details or contributed to the testing. So I will try to explain:
You can activate additional reporting functions for the dimmer by changing its configuration parameters and afterwards excluding and reincluding the device to the network. The parameters 100 and 101 allow to enable/disable the endpoints I2/I3 (which would allow you for example to connect another switch or binary sensor to the dimmer device on the physical inputs I2 or I3 and report their status changes to the controller). Another option is to connect a temperature sensor which also then represents an additional endpoint.
Yes, one of the 3 options to acitivate additional endpoints as stated above. (I2, I3, temperature sensor)
Correct, the dimmer performs its main original task (=dimming light) excellent, even with very low LED loads
This depends indeed from several criteria: The Z-Wave-Bind version you are using (or have used) to include the device and the activated (or not activated) endpoints on the device. From my experience:
Z-Wave Snapshot binding (non dev version): works fine for endpoint 0 (switch_dimmer) in any case (with or without activated additional endpoints) , but never for the additional endpoints.
Z-Wave Dev Binding before 20180102 (my latest before was 20171230): works fine for endpoint 0 (switch_dimmer) in any case (with or without activated additional endpoints) , but never for the additional endpoints.
Z-Wave Dev Binding from 20180102 (the most recent dev version): Does NOT work for switch_dimmer if NO additional endpoints are activated. BUT: Works for switch_dimmer1 and additional endpoints as soon as at least one additional endpoint is activated.
These are at least my findings.
For a solution the last suitable solution discussed here is to reactivate the channel ‘Switch_Dimmer’ (which was deleted in the 20180102 dev version). This would allow people without additional endpoints to have everything work with channel switch_dimmer. Users with additional endpoints could use switch_dimmer1 (for the light) AND the additional endpoints.
However @chris has not yet published a new dev version with this workaround solution. But he wants to do this until tommorow.