I think they would be fine given those temps, as long as your brooder is warm enough, they are perfectly fine to be out in light winter weather once they're feathered out.
As far as ticks go, you will probably not see a huge benefit from the chickens since you will be running them in tractors. They basically can only affect the tick population in the area(s) they have access to. We never saw a drop in ticks on our farm until we started completely free ranging our laying hens. We had been raising meat birds in the pasture for several years and layers in a rotating fenced area, but it wasn't until we let the laying hens out, and then bam, there were zero ticks. So it does work, but maybe not in the way you are hoping.
Another factor to consider is daylight. December 22 being the shortest day of the year, it will take longer for broilers to grow out during the winter simply due to the number of hours of daylight in a day. They will have less time to eat, but they will be colder so that will cause them to eat more in order to get the necessary calories to keep warm. I would anticipate a slightly longer grow out and a slightly reduced feed conversion rate, but it might be worth it for you since your summers are so hot. That can cause similar issues.