I would probably buy a jacket in as similar pattern I could find and then do some heavy alterations. You could maybe find a pattern and build from scratch though.
As for fabric paint, I've always had good experiences with Jacquard fabric paint! But you could always try a few different kinds of paints on a swatch of spare fabric to test. For the gold detailing in the butterfly, you may even want to get a gold puffy paint to be able to really show off the little intricacies. Also, a tiny puffy paint tip might be easier to handle than messing with a thick brush and goopy paint. But definitely experiment to see what works best!!
Also, I don't know if this will help, but there's a cosplayer who did a beautiful version of Xianghua in the past and has several posts about the creation of her costume on her blog here: http://the-ocd.blogspot.com/search/label/xianghua
I know it's a different version of the Xianghua costume, but maybe you'll find some helpful tips/ideas!
Hope I helped! Best of luck!