My thoughts exactly! I had to re-read the whole thing a few times to actually understand it a little.
1. On page 51, black feathers suddenly started falling. The old guy is the father of the real "Kira Sakuya". I suppose Lucifer/Kira brought the soul of the real Kira Sakuya to see his father. And the thought "..so are you happy now?" was probably said by Lucifer/Kira in hopes that the old man finally achieves peace of the mind.
2. I think they ARE Katan and Rociel. Just that those are probably their souls. They were probably there to try and help out Setsuna with the last bit of their power.
3. As for Setsuna's wings, I think he exhausted his power and Alexiel left his body. Alexiel was seen embracing Lucifer at the end and that was definitely not Setsuna's body. Setsuna was originally a soul created and modified by Alexiel to be the perfect being. Thus, they were both seperate beings from the start. When Alexiel left, his wings *or rather Alexiel's wings* would be gone and he would have no more powers. He would return to being a normal human.
4. On page 32, it didn't really seem like Setsuna was talking alone. I think it was a conversation between Rociel and Setsuna. Rociel probably helped return Sara to Earth knowing that Setsuna could escape on his own safely.
5. Well.. Adam Kadamon did say that the Heaven and Hell thing was there only because they thought of it that way. If they thought of it as one big barren land, it would be just like another place for them to develop. I think Kurai meant she would create her own Empire of Evils along with Noise. And Belial did say "Oh, Now he tells us." and stopped fighting.
6. From the scene, she did end up where she died.
7. Alexiel's body is under the guard of Uriel until her soul returns to her body. As for Gabriel, her body was left back in the garden *or something* a long time ago after Sara went back to her own body.
8. Frankly, I have no idea why Lucifer has 4 wings either.
But the first "God" he killed was not "God". It was explained in the 2nd last chapter - "No one has ever seen the true form of God. That was a form that the people have perceived as how 'God' would look like." So, only the 2nd "God" he killed was the real "God".
I think Lucifer didn't want to consider himself as Kira so that Setsuna would not hesitate to put the sword through "God" while risking his (Lucifer's/Kira's) life. Another alternatif would be Lucifer wanted Setsuna to live with the fact that he (Lucifer/Kira) cannot be with him (Setsuna) anymore.
Oh well.. That's what I think. I think the most confusing part is the part where Rociel and Katan are seen in the background.
Either way I look at it, it doesn't really seem to make much sense. haha.