In my version the sleeves are mislabelled. Right sleeve is actually left sleeve and vice versa.

My gauge was off. It turned out too small. So my son got lucky, he is skinnier.
My row gauge was even farther off. So I did a provisional cast on for all pieces and knit them to fit later.
Considering my gauge and reading the notes of other knitters. I simply repeated a few rows of the yoke without decreases. After the shaping of the neckline I kept on knitting in black with decreases until the neckline fit my purposes.
All in all it turned out pretty amazing.
I’m definitly knitting another one.