@Killjoy - Dig your voice - this is a really good song, I can hear a few artists on this forum that would suit your style as BVocalists.
Structurally everything is fine, like the rubato just before the 2nd chorus. Love the 'rhtytmn of the "I beleive in you"
Just a few ideas...Go a bit easy on the breathy ness, it sounds a little like you've just finished a 100m sprint, just turn it down a bit.
Reduce the reverb, add delay but not much at all, the voice is drowning and it really doesn't need to when you only have piano behind it.
As
@Bostonfan2 says well planned close harmonies would go very well, they might even be enough rather than more instruments, it does kind of sit well on it's own.
With many epic songs, you might think about chnaging the key of the verse once it's established in the last part of the song - think of 'Living on a prayer' just another way to add just a bit of contrast.
you have superb ideas, keep em coming.