FRONT:
(for future ref: the ribbing part should be done with 3.5mm needles, then switch to 4.5 needles when starting the stockinette)
Work with normal needles in size 4.5: CO 120 sts, work 2/2 rib for ~7cm, then continue in stockinette until reaching 15cm.
At this point change to needles 3.5 for waist shaping; work until ~30cm in stockinette.
Switch back to needles 4.5 and continue in stockinette.
At 39cm start the sleeve shaping (armholes):
on the RS (right side) cast off 6 sts on each side; cast off one extra st at each RS row for 6 times.
At the 6th time (~43cm) start dividing for the V neck:
cast off the central 5 sts (there should be ~47 sts remaining on each side).
Continue casting off 1 on the side for the sleeve for another 4 rows on RS and 1 on the centre (V neck) for another 15 rows on RS.
Cast off all remaining sts and proceed with the half side left on hold.

BACK:
Proceed similarly to the front, except leave out the neck shaping.

EDGES:
Sew up front and back with invisible seams (mattress stitch), with circular needles 4mm/40cm pick up sts along sleeves and neck and create a 2/2 rib edge.

NECK:
V-neck with central decrease and hemming (=double fabric, if not too bulky) in 2/2 rib. Edit: decided against the double fabric because the rib would be too bulky once doubled. Made single 2/2 rib and bound off fairly tightly to avoid a loose neck edge.

ARMHOLE EDGES
Pick up sts around the armholes. Knit in 2/2 rib for total 10 rows (incl. the picked sts row and the bind off row).

As a reference, I found useful information in: The Knitter’s Book of Sweater Patterns by Ann Budd.

I wanted to make a sweater, design the sleeves, as well as the body. Using these sources as a reference:

• The Knitter’s Book of Sweater Patterns (Ann Budd)
• Set-In Sleeves - a Love Affair (Pam Allen, in Interweave Knits Winter 2007)

EDIT: it’s staying as a vest. Good for layering while working from home.

HOW TO PICK UP STS FOR ARMHOLE:
https://ysolda.com/blogs/journal/picking-up-sleeves-glenmore