Yikes. Where do you live, Siberia? Plus that's about £800 worth of kit.
For anything down to about -5, I wear bib longs, merino t-shirt, winter jersey, soft shell jacket, packable rain jacket (if wet), winter gloves, overshoes, merino buff.
Agree with your merino socks selection 100% though. Worth the money. Also thinking about some winter boots while they are on sale.