Hi there Mollie!
I'm in Tucson AZ and my serama have done just fine with the swing from extreme heat to freezing temps at night in winter. They justfind shade, dust bathe in the cool dirt, and cozy up in their wind protected coop in the winter.
About their multi-roo temperament, in my experience it depends on the individual roosters personalities. I had one that couldn't stand other roosters, my current leader boy has no problem with other roosters who can submit, but he has to be the alpha.
I have also had lots of guys who were happy to live under the rule of another roo. I think they are more likely to get along with other roosters than other breeds might be but it still is an individual thing.
They are great little chickens! Originally I wanted to focus on BLRW but once I got serama I fell in love with the breed and can't imagine ever NOT having seramas. They are by far my favorite birds. I can't wait to see pictures once you get some!