Actually pinning the pleats was a lot easier than I thought.
When I was making my solid color kilt I had to be very careful with the measurements of the pleats to make sure that they didn't get crooked, but with the plaid, all I had to do was follow the pattern. I stitched every pleat on the edge (on the front) and it took me about 3 hours to do stitch and pin.

After checking for size, I will want to flip it over and stitch the other side of the pleats to make sure they lie flat.

Once that's done, I'll start the inner apron.