baw61983 - Tinkerbell Jesus Doctor - my name for when the Doctor goes all glow-and-float in Last of the Time Lords. Can't decide if it leans more towards messianic imagery or "clap your hands if you believe" but either way, it's not my favorite scene. Had to watch it to get good screencaps of Lucy's dress, though.
FBOBoss- Maybe it would help to think of it as if you were making a wrap shirt, and a regular skirt - then you sew them together. It may look confusing but it's really not difficult to make a garment that wraps at the top but not the bottom. The top is a fixed wrap - it overlaps, but you don't actually tie and untie it each time. The sash also appears to be sewn on, basically it's the waist band of the dress, with extra material flowing off to make the long tie.
Look at the dress here - http://tinyurl.com/ykp8dr5
Similar design, just drop the waist a few inches. The bodice has a wrap and plunge, then there's the waist band, then the plain skirt.
As far as buttons in the back - I never noticed them, but at a guess based on 99.9% of modern fashion I'd say false buttons concealing a hidden zipper.
Hope this and my previous post here are helpful. As much as I've analyzed the dress I almost feel like making one myself.
The triumph of intellect and romance over brute force and cynicism.