Hi and welcome back! You have lots of questions and concerns, which is great. I just picked up on this one:
Your concern was about them being more heat tolerant than chickens. But my concern is for their safety. I have chickens, not ducks, but where predators are concerned, their needs are pretty much the same: somebody has to lock them into a safe environment about dusk, and release them in the morning. Here in SE MO we have raccoons, opossums, skunks, snakes, coyotes, foxes, dogs and feral cats. Where you are, you may also have rats, bobcats, mink, weasels, fishers, cougars and bears. Domesticated birds need a predator-safe enclosure to protect them from these marauders, particularly at night. If you take off for several days and nights, leaving your birds to fend for themselves, you may not have any birds to come back to.