I wonder if there will be any snow/winter type creatures in that area?
I'd guess so, and yes, I'd say the snow is probably permanent, which I am fine with, since as has been said, players probably won't be playing the game for enough in-game days to have seasons mean anything, and it would ultimately just be more complex programming than it's worth, plus, that would mean that you could potentially play through the entire game without seeing any snow if you didn't go there during the winter months, and never seeing the most unique features of a place (After all, I'd imagine that snow will be rather limited in the game, probably only in the region Jacobstown is located in.)
As for Marcus being a companion, I'd say that if that were
not the case, it would be quite a missed oportunity, so it would seem pretty illogical for Obsidian not to do that.
I wonder if Marcus will tell any stories about his experiences with the Chosen One, though?
If I'm not mistaken, nuclear winter wouldn't happen all of the sudden in a concentrated area over 200 years after a nuclear war. It would be much more widespread and it would happen quicker than 200 years.
I think you're correct, I'm pretty sure that nuclear winter would be more or less a global thing, plus, the idea behind nuclear winter is that particles would be sent into the atmosphere which would then block out sunlight, causing surface tempertures to drop due to the lack of sunlight, the skies look too clear in that screenshot to me, if memory serves me right.