Welcome!
The other reason to add light in the winter is so they can eat more. They can't eat in the dark and they can eat only so much at over a given timeframe. The colder it gets, the more food they need. At some point they don't have enough daylight length to eat enough.
I don't know the details of how cold/how dark. I'm in the ballpark of as far north as you but I don't expect to get as cold. I'm sure I don't need extra lighting but I am going to make sure they always have food and, especially, that they always go to roost with a full crop.
I think it also matters how much natural light there is in the coop. I can open nearly the entire west wall of my coop; I've noticed a difference in when they go to roost based on whether those doors are open or not. One day won't change their timing but several days in a row will. If your coop doesn't have many winows or they are all on either the east or west sides, it might matter for this.
About your heater - have you considered the amount of dust in a chicken coop? It tends to be flammable as well as clog fans and such. I don't know much about the different kinds of radiant heaters so am not sure how much this might be an issue in your situation. I do know of some barn fires caused by dust on heat lamp bulbs.