This is a beautiful classic orchestration ! A very pleasant journey :)
The Astral plane is such a cool atmospheric piece and works really well with the landscape you described.
I was surprised by what you acheived Nightmare, it's not heavy and stressfull as I imagined from the title. It's subtle and disturbing, perfect in the mood of your ost. It makes the whole Ost very cohesive.
Then, great nostalgic ending, magnificent !
Ps: I love your friend's artwork !