You can do some test shots to try out the frosty breath effect and see for yourself how it looks. And yeah, I forgot about the sound. It is more important than the visuals. Get a great sound mixer.
Don't use the fake frosty breath. It didn't look great in The Social Network, and I'm pretty sure it won't look good here. Just shoot in November, if you want that effect.
Other than that, get a good crew. That's really important. And your friends can't act.