A simple "neck up" as we call them, certainly makes a real difference in stopping cold air gong around neck.
I use a balaclava at a certain point also, as most winter activity people do.
Re hands. As you guys ride in winter, you probably use these, but I have an old pair of mitt shells, ie no insulation, that I put over various gloves or mitts, and cut the wind it makes all the difference for hand warmth.
I layer different stuff inside, but main advantage is that they pack flat and weigh very little.
Bought them at mec ages ago.
I've seen folks using those poggie things, for winter riding, attached to bars and you slip hands into.
Bulky but effective I imagine.
But you have to take into account space and weight....
Ps, ortlieb make oversize rear panniers, 70 litres I believe, great for bulky but not super heavy stuff.
Hey, you never said what bikes, does that mean you don't have them yet or undecided?
Have you toured before?