Wow, that chorus transition is amazing! The chorus itself is really nice too.
As for the feedback you asked for, I'd change the composition in the following ways:
I'd wait with adding the drum track untill the start of the chorus, then continue to use it throughout the rest of the song. I feel it takes away from the build up now. I would also add a base during the chorusses, and indeed add some more strings.
I wouldn't add an electric guitar, you're singing to the piano, not to the guitar
Other than that it really works man, you've got a great voice!