How to (or can you) pair motion paths to slider?

To move the slider and have the shape move gradually and smoothly around the path, not really.

What you can do is to break the path into separate segments, and write triggers:

If you only want one slider move, and one motion path move, the triggers are relatively easy: Move object on motion path 1 when Slider Variable changes if Slider Variable >= 1. Move object on motion path 2 when Motion path 1 completes if Slider Variable >= 2, etc.

If you want multiple forward moves, you also need to keep track of the current location, and if you want to move back and forth, it is much more complicated.  See the attached sample for a couple of options. The problem with the slider is that if it is moved too fast, it gets ahead of the motion paths, even if they are set to minimum time. The arrows might be a better option.

The more (and shorter) segments you have, the smoother the motion will be. It depends on how much you want to put into it.