I never cut a steerer unless I've found a permanent position and know I'll never need the additional length again. Even then I leave 5mm or so of wiggle room in case stufff changes in the future.

I remember back in the days of threaded forks, some people would trim their fork for a low profile headset, and be SOL if later they wanted a taller one like Campy or CK.

Add a spacer wither below or above the stem and leave your options open.

As far as adjustment goes, remember that any adjustment is impossible unless the stem/spacer stack is taller than the steerer by a few millimeters. Otherwise the top cap will beach out on the top of the steerer as you try to tighten the headset.