RE; 'Poof', the correct shape for Ciel's skirt should be something similar to the second or third picture down on this page
, and the petticoat would have had a stiff ruffle around the bottom for more bottom poof. The front and around the hips should be fairly neat.
Honestly, I have not met a person that bustles look bad on, so I would give some back padding a go even if you're not going to do the full underpinnings. I have seen the dress done with no petticoats or anything underneath and... well, it looked a bit sad, like it had wilted.
RE; binding, it might depend on how large you are, since the dress doesn't come up high enough to cover more hardcore binding methods, but do the best you can.