I would like to know this as well.
As far as I know, the Ortho Width property of the camera basically sets the width of the visible scene in unreal units. You need to convert that into pixels. I’m not sure if there is a global conversion value you can use or access somehow. There is a default Pixels Per Unit value in the Paper2D project settings, but that’s just a default value that is set to your newly created sprites. So maybe you’ll just have to decide on a value for your game and hard code that in your camera setup code. E.g. for an iPhone game in portrait mode and a conversion value of 1.28 you would have (640 pixels) / (1.28 pixels/unit) = 500 units of Ortho Width.
I’m not sure about the best workflow for supporting different resolutions either and I hope someone with more experience can answer that for us. Thanks!