We're in the deep-freeze, too, right now with lows at -20c. My coop is no longer insulated (ripped it all out due to rats making a mess of it) and i have not sealed off the 12"x32" grate that serves as the vent. Not only do i still have birds (young cochins and brahmas) wishing to roost outdoors...
I had a silkie once. If ever there was a "winter chicken", it was her! She was the only one who cared to venture into the snow and the only one smart enough to know that green stuff hid underneath it ;) Unfortunately, she was lost to a predator (who broke into the coop and killed a bunch of...
Both those breeds are cold hardy. They could happily live in Alaska without added heat, I'm sure! I'd be more worried about how they'll handle summers down where you are. As for roosting, they will when they're ready. I've had some start roosting at 4 weeks, others not until about 12.
If they have lots of vertical space they might be okay. My coop is only 6x8 but it's also 8' high with 4' of one wall all nesting shelves and the back 4x6 section is a network of criss-crossed roosts from 2' all the way up to the ceiling. I've had as many as 30 large breed chickens - always at...
I don't plan on using the heat lamp this year. All the birds I have left are all cold hardy breeds so they should be fine. We do get nasty windchills off the water but my coop always seems to be quite cozy no matter the weather.