I'm actually in the process of making a 3D balcony.
Sweet! There's one or two 3d caves story stages in the vault, but not a fan of the way they look in 3d, i prefer the 2d style for cave story. still, good luck, and I hope it turns out well.
If you haven't already animated the background, feel free to borrow the one from mine, no sense reinventing the wheel after all