Welcome, I am new also, but I do have lots of duck experience. You don't need the boxes, but certain breeds prefer the box and others like to hide their nests. My muscovy and runner ducks tend to hide their nests, while my cayuga and east indies won't lay anywhere but their boxes. I hope this helps.
Muscovy are the only ducks that I know of that will nest very high. I had to move several eggs from a tree that is in my breeding pen, but when I locked the duck up that was laying I guess she figured out that was not a good thing, because she never tried to lay in the tree again. But my muscovy love to roost in the tree at night.