That looks gorgeous btw! LOL Now down to business of where you may want to start. I am just going to assume you have an idea how a Kimono/robes are worn. It's similar.
For me, I would begin from the top part of the dress itself, anything that is not waist down because there is just a lot going on... The different colors and patterns you see on the clothes references of course indicates the different layers she's wearing inside. So excluding that obi-like sash thing around her waist, she's wearing 3 to 4 layers inside just on top. I roughly drew out how I would separate the top parts just to give you an idea of where to start (from learning of my momís sewing of our traditional clothes, itís the same idea as well). The magenta/dark hot pink color could be like a vest kind of thing. The inside that is 2/3 layers could be cut like a jacket (just putting it in terms to describe it as easily as I can). I wouldn't worry how long the jacket would be because it'll be tied around your waist and hidden under all of 'obi' part of the clothes, the skirts would be tied around the same area and the obi of course would hide all of those flaws. And depending on how hot you want to be in the costume, you can make all of the layers separate or just sew it together for easy of putting on the cosplay (and itís cooler this way).
There will be a lot of guessing on the cutting of the shape and alternating them, but Iím sure youíll be able to do it as the art reference gives you a great idea of how it looks from the back and front! Good luck!
My sketch here
I hope I helped some and gave you some ideas of how/where to start!