Rounds 1-4 of chart A I worked 1 x 1 ribbed colourwork. Knits in CC, purls in mc in 3.75mm.

Rounds 5-7 of chart A I worked seed stitch in 3.25mm.

(adjustments made to ensure the edge does not roll, I originally started the project as written and my gut told me the amount of curling would not block our sufficiently to my liking)

Stockinette rounds were worked with a 3.75mm needle.
Colourwork rounds worked with a 4mm needle.

The top edge was worked the same as the bottom with rounds 11-13 of chart c in seed stitch, and rounds 14-17 in 1 x 1 rib.
I worked one round of mc, and then the round of purl so my cc knit columns looked clean.