If you like it, go for it!
But you might want to alter it slightly so the wings and like you said, the tail so that they don't stick out so far. I don't have any advice on how to help you make it though. As long as the finished product is light and durable enough for the con, I think you'll be alright. And I couldn't see the dress all to well, but it looked like there was a lot of detail on some of it. But it looks like a fun challenge. Hope you do it!