I was able to get this achievement by finishing this level on 'easy'. Keep the perimeter of the generator clear of anything but tents, you will need the space! Build any buildings you need toward the very back and connect with paths. Gather materials starting from the generator area working your way out and clear that area as soon as possible.
I had 5 research buildings as soon as possible (after all tents were built). Focus research on keeping your original group warm with generator efficiency, beacon, and medical. Employ them, keep them warm, and feed them as usual. Then focus on max wood generation and kilns (knock 2 achievements out this way).
As groups come in, make sure your generator gets expanded and more powerful, plus keep focusing on medical until it's maxed, you will need it for a large group of infected people and you do not want to get behind. I had 8 infirmaries toward the end.
I don't have time to write a full guide yet. PM me if you get stuck and I'll try to help.