1-Funny idea. I think the shot would have worked better with more sky (to subtly put us in mind of flying, levitating); and I think the white vignette clashes, because normally I see the white vignette look applied to more formal, less comical images.
2-I usually consider it a kind of wedding sin to cut off the Bride's dress in this way. Aside from closer crops (waist up for example), I normally consider the dress an extension of her and try not to cut it off at least for posed shots (I often make the mistake though !). I like what you have done in framing her with the tree arching over her. The next time you shoot something like this, I'd recommend trying to expose as you have then add an off-cam flash to light her up. I wish she popped a little more in this image; this method would help achieve that.
3-Nice. I like this. Biggest thing holding it back in my mind is color balance. Hopefully you shot in RAW; I'd recommend making the image far more warm (so in the direction of yellow).