Originally Posted by FBinNY

Absolutely no problem leaving the steerer overly long with a ton of spacers above, until you decide where to cut. Most experienced mechanic would suggest doing this, based on the premise that once cut, you can't undo that. I've known folks to cut steerers twice. Once when they think they know what they need, and a second time months later when they know.

The need for a thin spacer under the stem depends on the stem and headset. The first item above the centering cone has to touch only that. Most stems would be OK, but I have seen stem/headse combinations that want ta spacer in between.