Yes, but so does voltage. Nuclear spin is special in that you can have superpositions, but you don't necessarily have to have them, in which case it's a perfectly valid way of storing a binary decision.As for nuclear spin, well that would yield more than 2 states.
Yes, it is. You classify the possible states of the basic element of your medium (a magnetic particle, a dot on the optical medium, a time interval on the electrical line, a single atom, ...) into three classes: 0, 1, and (possibly) invalid. Then you build the technical means to measure and set these, with voltage as the common language of all such components. Now, these technical means may be extremely involved, very complex, and all that, but in the end it still just translates one representation into another. Measuring magnetism should be your area of expertise, not mine.But it's not straightforward.