Just this week I bought the same bivy also to use as a vbl. I am hoping to get out camping in late February to give my system a shake down spin. I have a army surplus gore tex bivy sack that I bought via ebay for under $50. To date I've not had any condensation in the bivy, but have yet to use it in the winter conditions.

I bought the emergency bivy instead of the thermo-lite bivy. What's the difference?

Basically my system will be the same as yours. Down bag, vbl, thermarest (and possibly a foam pad) and a gore tex bivy sack.