The jumper is knitted in one piece and has no seams except for the short gap on the armholes. Even this you could knit together. For me it was easier to sew it.
I used self spun yarn from fine merino wool. For reworking I recommend yarn with a length of approx. 300 m / 100 g such as NORO Silk Garden Sock Yarn.
The reference for the material consumption for size 74/80 is 92 g. The smaller size is approx. 85 g, so you need more for the other sizes, for which I cannot (yet) give more precise information.