How to use AddOutputVariable measure?

I am using the AddOutputVariable measure but I have some questions?

What is the difference between using the measure and Output Variables Tab in Openstudio?
I notice that e+ has more output variables that the list in the Output Variables tab. So I am exporting from OS the IDF file and run the simulation once in e+. After the first run I open the RDD file and see what output variables are available and copy the names in OpenStudio AddOutputVariable measure then run the simulation again in OS.Is there a more efficient way to do it?
I did the same with AddMeter Measure and MDD file but I cannot see the meter result in OS Results Viewer.

There is no difference. Adding the rest of the variables to the GUI is just far down the TODO list.
The .rdd file is created whenever you run the simulation through OpenStudio as well. Just run the simulation like you normally would, then find the eplusout.rdd file in the MyModelName\run\5-EnergyPlus-0 directory. Also, many of the available variables stay the same between different models, so you can look at any old .rdd file you have laying around to copy from and most of the time you'll be fine. Requesting variables that aren't available will at worst throw warnings during the E+ run.
Do you see the Electricity:Facility meter in ResultsViewer? I would double-check two things first:
1. The meter you are adding actually shows up correctly in the .idf file.
2. That there are no warnings about this meter in the eplusout.err file.