All of your questions were answered by others, but you failed to mention the big'un.
The money bin is 3 cubic acres of money. Acres are a unit of area, meaning they have two dimensions. Cubic measurements, three dimensions, are typically by notated by length, width, height, one dimensional measurements, because that way 1 by 1 by 1 = 3. To be a cubic something of area notation, a theoretical "cubic acre" would have to have SIX dimensions. Even in cartoon land, we've only seen 4 dimensions, and barring Gyro Gearloose, have no ability to navigate freely that fourth dimension. Which means that either McDuck is so rich 1) he's gotten access to dimension-hopping storage and measuring devices, or b) he's got so much money, the sheer amount of it in one place BROKE REALITY.