Hi, welcome to the forum. Glad you joined.
Our night time lows average from 25 degrees to 35.
Personally I worry about extremes more than averages, but I understand that's what you have to plan on. Just be flexible to adjust if you need to.
Is this too cold to transition the chicks to at 6 weeks?
Probably not. I've had chicks younger than that go through nights in the mid 20's Fahrenheit. But what does the coop look like? Mine had really great ventilation up high but great wind protection down low where they were. Also, mine had been raised in my brooder in the coop. It was big enough and well ventilated enough that they had acclimated. I kept one end toasty warm but sometimes the other end might have frost in it.
I put chicks in my brooder in the coop straight out of the incubator or from the post office, whether it is below freezing or in the heat of summer. I find that as long as you keep one location warm enough in the coldest conditions and one location cool enough in the warmest conditions they are very good at managing that themselves. As long as you don't have older chickens out there to cause integration issues you can pretty much move them out there any time. One of the big challenges is the temperature swings. I've seen it go from below freeing to in the 70's within 36 hours. Another potential issue is your heat source. There are a lot of different ways to provide heat, they can all work. The chicks grow fast. Can your heat source handle them when they grow? If you are brooding them in below freezing temperatures how do you keep the water thawed? There can be issues.
If I do transition them out in these temperatures would you use a heat source until it is in the 40’s at night?
No, I'd quit using it when they no longer use it at night. I use a heat lamp and even when they don't need it they tend to sleep in a warm spot anyway. If you use a heat mat or heat plate the heated area is a lot more restricted. You might be surprised at how young they stop using that heat at night.