We live in West Central Texas and our temps this time of year dance with triple digits daily. The last few days it has consistently topped out around 103 or above. We have Cayugas, Blue Swedish, Khaki Campbells, one Runner and one mixed breed. They all seem to do fine in the heat so long as they have plenty of water to drink and splash in and plenty of shade. We do have a pretty steady wind here as well which probably helps us.
Ratio of male to female should never be below one male to every 5 or more females. Anything else can result in the females being overbred which can lead to injury or fatality. And, yes drakes will fight with roosters, don't know if it is actually the other way around. We had to finally create a space apart for the chickens and ducks and geese because everyone seemed intent on killing each other. Also, a drake mating with a hen (chicken) can kill the chicken. It is an anatomy thing.
Duck eggs are actually very good. Frying them can lead to a hard egg white if cooked to hot and fast but as scramble or for baking they can not be beat. They make great omelets also. My favorite is scrambled with serrano peppers, onions, tomatoes and some cheese on top. Or scrambled with chorizo is also very good. They do tend to have higher nutritional values and less water in the albumin. I have read that a person with chicken egg allergies can eat duck eggs but I don't know that to be true.
This is all based on my experience with my ducks. I know there are stories here on BYC that differ. Whatever, just enjoy your ducks if you get them. There really are a treasure.
PS our Cayugas and Khakis are the real egg layers in the bunch.