I like your interpretation of the last track :) The motion between the two chords doesn't feel totally resolved but still implies a sense breaking free.
I am like you so I couldn't resist using music boxes! =D Especially for that song that mixes different ideas and feelings somehow already connected. It felt like a good glue to use.
It's funny that your mention the openness of the introduction in the second song because the first repeated chord is indeed very open. And I used it as the base link of my ost.
I didn't go for a melodic leitmotiv this time, this one chord is actually played on the opening of first track (violins and voices). At the end of 3rd track too and shape the last song. Haha I went so much in detail with this response ^^.
Thank you very much for your feedback and telling me about your interpretation!