All reasonable questions. No apologies necessary.
Some keep ducks and chickens together - you just need to remember ducks are a little different. They nest on the ground, so don't put them under the roost where they'll get dropped on. They cannot be as neat with water, so separate duck and chicken waterers are needed.
At least 25 sf per duck is a good idea - more is better. Some people let their ducks roam, but they are quite susceptible to predators. Mine plan in the gardens, but while I am nearby. When I am not, they spend time in the 10'x16' day pen attached to their 64sf house and porch. At night, they are in the house/porch with electric fence on.
If you raise them from day-olds they will most likely stay nearby, older ducks sometimes try to go "home" from the new place.
Ducks need water they can bathe in, and you need to plan for their swimming area - slight slope, well drained, no really, it needs to be well drained, with pea gravel around it (a few inches in depth at least). They don't need a pond, a kiddie pool will do but they need to be able to easily get in and out of it, and ducklings ought never be left in swimming water unattended.
Ducklings, by the way, need three times the niacin as chicks.
I'll let others chime in here.