[PvK]

I'll let more expert folks cover the details, but on point 1), I think units regain consciousness as soon as they go back below 100 fatigue - they don't have to rest all the way back to 0.

As for casting the 100-fatigue spells, it will tend to knock out a caster with the same level of power as the spell required. As you noted though, having more power cuts the fatigue to half or better.

PvK