To make this pattern seamless, cast on the front and back stitches less 4 stitches to account for the seams that you won’t be needing. Place side markers, denoting the BOR as the start of the back. Join to work in the round. Knit as as written.

When you separate for sleeves, put front stitches on waste yarn and knit back as written but do not bind off; keep back stitches on a spare needle. Put front stitches back on needle and knit as written but do not bind off.

To join shoulder seams, put back stitches and front stitches on needles and with right sides facing and using a 3rd needle, bind off shoulder seam using the 3 needle technique, then bind off center back stitches, then bind off next shoulder seam.

Knit arm and neck ribbing in the round. I do my neck ribbing a little differently than the pattern. I use a center stitch at the V that is always a knit stitch. On either side of the center stitch, and only on every other row, I do this decrease: K2togTBL, k center stitch, K2tog. It just gives it a little more professional look.