Hmm... I think not with the black parts...
You might be right on the dress, thought I have to admit I have thought more of wearing comfort in that matter.
One option would of course to strengthen the cloth to make it more stiff. The other to also make it out of craft foam.
I'm afraid I do not know what foamcore is, so I can't answer that question.
As for colors on cloth: There are specific colors (looking similar to acryl colors) just for clothes. There is a separate brand for dark clothes, so if you decide to make the black parts out of cloth and want to apply the white pattern to it, I recommend really going for the slightly more expensive color that is specific for dark fabric. I've tried to save costs once, that was a good enough lection for me not to attempt that again. ^^°
Compression Shirt Supporter.
DON'T use ACE for binding. It's BAD for your health and uncomfortable.