A lot of folks have mixed breeds and they'll have a few silkies too. I'm not familiar with too many problems doing that as the silkies sort of stick together I've heard. I would just make sure if you get some that you get at least 4-5 as there's strength in numbers.
As for the heat, they do suffer just a bit more than most from it. We get a couple of weeks of 100F with high humidity up here in Wisconsin in the summer. They free-range and I'll find them under the Hostas usually. I always have a bucket of water (usually with Hydro Hen in it) out in the shade for them and put ice cubes in it a couple of times a day when it's that hot. The dogs and cats like that too.