The construction went pretty much as planned once I had the bodice fit down.
I used a thrifted navy fabric with a slight zigzag texture to it (no idea what you'd call it - jacquard?). From a burn test, there's not a natural fibre to be seen, but it holds a crease pretty well which was important for the inverted box pleats in the skirt. I bought 1/2m of red cotton, thread and a zip, which was the sum total of extra spends on this dress - it's a cheapie!
I used the bodice of NL 6000, as well as the short sleeve.
I debated lining it as I can be a bit sensitive to certain fabrics, but it's actually fine. I ditched the facings and used bias tape instead and it was so much easier - I think I'm going to do this much more in future!
For the skirt, I started with Colette patterns Peony as a base. It's an a-line shape with gathers instead of darts so I thought I could work with it (and I had already altered it for length). 2" wide pleats seemed about right to me so I went with that. I traced another copy of the pattern and marked on the pattern where the waist darts (back and front) hit the skirt. Slashing up this line, I added 1" on each side of the slash plus seam allowances. I then drew out a contrast piece 2" wide (plus seam allowances) x the length of the skirt.
I ended up with loads of skinny pieces to sew together so I used french seams as I thought it would look better. Often the insides of skirts can be seen and with the contrast between the two colours, I wanted it to look neat.
I then marked the fold line on the navy fabric and pressed it like mad (pressing was a key feature of this make!). I folded the navy fabric over and stitched the folds together and pinned and basted them flat, before attaching the skirt to the bodice. On the muslin, I had shaved a bit off at the waist to make it the same size as the bodice (taking out the width that the gathers would have in the original Peony pattern) but once it was stitched, I thought the skirt was a bit poofy so I took in the side seams by about 1/2" at the hips widening to about 3" at the hem.
I was cursing the french seams when I was hemming - that's a lot of fabric to stitch down flat! But my little machine managed it fine.
As for the insides, I was undecided on seam finish as the fabric was too thick for my usual turn and stitch - it would have made the seams bulky and visible from the outside. I was assured by the lovely #sewcialists on Twitter, that pinking was vintage rather than lazy, so I went with that! French seams on the skirt panels, and I bound the waist seam (badly!) with the same red bias binding I used for the neck. It's not my neatest zip insertion but I don't think the fabric would have held up to unpicking and restitching.
Finally I stitched on buttons at the top of the front pleats and made a belt which fastens on like the original dress: