1.I think you meant with magnitudes, since complex numbers are not ordered as is, though their magnitudes, being real, are ordered. Otherwise, everything looks correct.1/2 <z and 1/4 < z

2. Looks correct.

3. You forgot one term, I think: the delta function as the inverse z transform of 1. Otherwise, it looks correct.

You do know that WolframAlpha can do inverse Z transforms? Format would look like this:

InverseZTransform[f(z),z,n]

Here's a simple example.

So you can check your work that way.