3.5mm for gauge, 3mm for ribbings.

All made exactly to pattern.
Finished weight, exactly 100g, 700m (before blocking)

Coast has zero stretch, and I did find the P3tog a bit tight. I changed to using a smaller (3mm) tip on the left hand needle, and knitted the kyok very loosely (as I would when knitting Estonian nupps… stretching the loops out by pulling the RH needle upwards and outwards).
I did the P3togs right on the tips of my needles.
That helped enormously.

Measurements, before blocking:
Bust, 38”
Length (from top of shoulder next to neck), 22.5”
Underarm to hem, 13.75”
Inside sleeve, 2”