I'm not sure optoisolators will do anything but screw up the waveforms and timing. They are ultra-slow and quite weak, in general, even the darlingtons.

IF there's a common ground, then there's no benefit in isolators. All you have to do learn what kind of motor you have and what it takes to drive it. I've never used anything much more complicated than a handful of npn transistors, or maybe mosfets, even for motors I could hardly lift. You should ask yourself WHY this motor is "bipolar" and why you're using it. If there's no good reason then a unipolar type is probably preferable and much easier to grok. There are good reasons for using bipolars, but you have to have a good reason.

The Jones reference shows how to deal with bipolar motors, so that should help.

RE