It depends upon where the expander plug sits in the steerer tube. If the expander plug sits with its top level with the top of the steerer, then you should not put spacers above the stem. The stem should clamp precisely where the plug sits. If the plug can be positioned down the steerer a little ways, then a spacer of that height can be used above the stem. Some forks like Easton's EC 90 XL require a spacer above the stem and actually provide one for that purpose. Others prohibit it. It all depends. I would follow manufacturer's directions.

As far as cutting the steerer tube, you can easily do it yourself with a hacksaw or even better yet, a Dremel tool. If you are like me, you will not get the perfectly clean edge that using a prescribed cutting guide will give, but I can't figure out how that matters. As long as it is not too uneven and the top cap is a couple of millimeters above the top of the stem, the system will work fine.