To make the sleeves I took a pattern that I already had and altered it to be a petal sleeve. I found the directions for making a normal sleeve pattern into a petal sleeve pattern. It was fairly easy since you overlap the fabric to fit. So the pattern piece does not have to be a perfect match for the existing sleeve.
I double sided the sleeve so that I could just sew the front and back to one another instead of having to hem the edge. It was SO much easier to just turn it around and iron it flat.
For the back panel I put the dress and put pins in the sides where I wanted the panel to reach. I Roughly measured how large the piece of fabric would need to be and cut some pieces that were larger than my measurements. I wanted a seem to be through the middle of the panel so that it could mirror the train on the dress bellow the bow. I hand sewed the panel in so that the stitching was not visible. Like the sleeves, I also sewed 2 pieces of fabric together so that I did not have to do any hemming, just turn and press.