I brood in the coop with a heat lamp when it is below freezing. I put chicks straight from the incubator into that 3' x 6' brooder regardless of how cold or hot it is outside. In winter I wrap it with clear plastic to hold in the heat but still have enough ventilation up high so the far end cools off. If I were brooding outside in the open instead of in the coop I'd use something more substantial than plastic over the wire mesh because of wind but don't really see any difference to what I'd do in the coop. The chicks don't care what temperature it is outside, it's that I have an area big enough for 20 chicks warm enough inside the brooder. The warm area isn't all that big and sometimes I have ice in the far end of the brooder.
For 7 chicks a heat plate could work but some manufacturers say they don't work below 50 degrees F so be careful. If set up right a heating pad could work really well for 7 chicks. That would probably be my preference for you. I had some experience brooding with the heat lamp in better weather, that helped me have more confidence in how to set it up for freezing weather.
I agree it is a lot easier as long as the flock and chicks can see each other. With the chicks growing up with the flock in the coop I typically open the brooder door at five weeks, that's how I integrate. But I think an important part of that is that I have sufficient room and weather that mine can be outdoors all day every day. @drangle I'm not sure how much room you have indoors and in Colorado you may not have the weather that they can use the outdoor space. It might be harder than what Finnie and I do. But integration is still a lot easier if they grow up with the flock.
