" am convinced that Luke's obscured face is from another shot. Why else would they show him with the face dark and the hood up?"

To show a visual similarity with the Emperor. And create unease in the viewer that Luke is perhaps turning to the dark side from the (presumably) regular 'messages' from his Father via the Force. A great beginning to the film in my opinion! The more I see it the more it already feels like it belongs to the beginning of Jedi and should be seen that way. Looking forward to some fan edits of this footage into the original film already ;)