DebinAZ- I'm in the Verde Valley and have 2 Americanas/Easter Eggers. I've found that they do well in the heat. They all suffer to some degree, though. My hen house/run are poorly shaded due to OLD trees. I take extra precautions for my flock, including keeping frozen gallon milk and water jugs in the hen house. I also put frozen 1/2 liter water bottles in their waterers daily (or even twice if it's really hot). If you have a well shaded area, I would imagine yours would do well.
As for getting chicks vs hens right now, if you watch cragislist, freecycle, the feed stores, etc, you can sometimes find older chicks/pullets or even laying hens. I 'think' in the coming months, there may be more freecycled or craigslist'd chicks because people will buy them for the "cute Easter chick" factor, then get bored with them.
Most of the feed stores around here will specify 'straight run' (not sexed) or sexed chicks. I got started with laying hens and am glad I did. But, many people will tell you to start with chicks. It's really more a matter of your comfort level.
And, finally, welcome to BYC! You'll find a wealth of valuable information and wonderful, helpful folks here!