Does lowering preveiw of multirez to max in this case to 0 mean more detail of the displacement map than lowering it to something like 2 or 3?
Yes, that's how it should work. Basically the preview value and the render value sets the spectrum of geometric detail for baking. If you do preview of 4 and a render of 5, there's not going to be much difference between the two levels. But set preview to 0 and render to 5 and the geometric difference is big.