Hey Hydronium,
So far I really like this piece. I think the color choices so far are good, and the composition could be good. I'd need to see it more finalized before I can say that though.
I only really edited her face. The nose is not readable, and looks like there is just a hole in her face. It can be fixed in like 5 seconds and a few pixels though. I added a highlight to the nose, too. I took a pixel off her cheek, and added midtones to the ear. Her chin seems too small, I moved it forward a bit and enlarged it.
Sorry I couldn't help with the dress.
One final thing, I think the piece will be much different depending on whether the guy is looking at the girl, or is looking at what she is looking at (the sunset?). So think about what it is you want.