Buy one size up in Ibex if it runs small for you.
Buy Icebreaker if you can't afford Ibex, but buy Ibex any time you can get it on sale. (check the Ibex Outlet and BackCountry.com and Sierra Trading Post and REI-Outlet)
Wear a bra under the wool. Ibex is coming out with wool bras this winter, but until then wear a regular bra.
Treat your wool t-shirt like you would any other t-shirt for layering. Put your favorite warm goodies on over it. It'll be just fine.
Wool just keeps on breathing, but how much vapor gets out your waterproof shell is entirely up to the SHELL. (not the wool)
When it's wet and in the cooler temps here in Seattle I like to ride in wool Ibex capris, wool socks, bra, wool longsleeve t-shirt, and wool sweater. I might put a shell on over the sweater if it's *really* raining, but tend not to. I generally wear just my PI visiblity vest cuz I sweat so much.
I have a wool helmet liner and wool gloves for those really cold days.

