Since it is from the hatchery then it is pretty safe to assume that this is still a Marans just blue instead of black. (Very unlikely to get a rare breed that the hatchery does not sell) As far as gender it is likely male, but at six weeks some female Marans can get this much...
From the description I would guess it was something that happened to the single chick, but just in case watch for chicks sleeping more, not eating well or unusual poo.
Make sure you double check the temperature that your incubator says vs. the actual temperature at the top of the eggs. Humidity has a bit more flexible. I have seen suggestions between 30-55 before lock down. The eggs should loose moisture. I dry hatch in a fairly humid environment. For...
Another source of calcium is feeding the egg shells back to the flock. It is not enough as the soul source, but might be enough when combined with the layer food being given.
This time of year drakes are at the peak of breeding season. They will pair off with duck hens if they were brooded with only ducks and have enough hens to pair with. If they were brooded with chickens, sometimes they are just as likely to try to get a chickens attention as a duck hens...
I don't know if your turken is dual purpose or of the meat variety, but it definitely sounds like heart issues. I am unaware of anything that can be done for her at this point. It may benefit the others to be fed like meat birds (kept for breeding) to lessen the chances of it happening to the...
What is the age of the bird? This will help with gender. If it is under 6 weeks the color/ waddle development is looking male.
As far as breed/color it appears to have a dilute meaning it is blue instead of black. I don't see any indication that it is not a Marans, but where did you get it...
Yes it is normal. Sometimes their combs don't even fit in the holes, but sometimes roosters don't want to sick their head in places instead of being on the lookout for predators. My roosters pick at the bits the hens spill and I have an oops hole smaller but no port from making my own feeder...
Wild Mallard duck behavior is to pair off and make nests this time of year. Domestic ducks still seek their own territory. Even after laying eggs in communal nests my ducks will seek a spot away from other pairs.
I would cautious about placing a single chick with ducklings. Ducklings grow much faster than chicks, splash water, and trample whatever is in the way.