Yarn held double, gauge is 16 sts on 10cm, so I change the stitchcount a bit.

CO 115 sts, 4 rows of ribbing (needles 6mm), 1knit row (needles 7mm).
Then a bit of short row shaping - 20 sts from center and then each time 10 sts more.
68 garters on height.
Fronts on 45 sts. On 61 garters start inc towards the neck shaping (inc 1 st every second row) , to connect fronts and back more smooth.
Sleeve stitches picked up from the body (50st) and knitted in the rounds. Dec after every 2nd garter (5x), then after every 3rd garter (2x) = 36 sts.

The way you should sew the pieces together according the pattern seems awkward (I tried and failed), the matress stitch is much better. Also picked stitches for the front rib from the garters “bumbs” not the “between the bumbs” (this is invisible from both sides).