Does the computer have both VGA and HDMI outputs? Do you know whether it can drive both outputs?
Openlp only supports two displays, so you are going to have to manually set up what goes on the third screen. I'd start a browser and then once you have browsed to the remote URL, drag it on to the third display, then make it full screen.
I'm not sure what you mean by notes for the Pastor...
Hth, Paul