Humans may dwell here

Do tornado spells have their damage reduced by resistances?

If you mean armor, then no.

What is the range of spells? I've noticed that it's only specified for Wave and Incinerate.

The range is infinite; you just need to be able to see the target.

What is the average range of bows and crossbows?

The maximum range is 30, but bows will deal reduced damage over the last 20% of the range.

What are the approximate penalties applied by armor if worn by a character with the "Combat Training" skill?

Light armor has no penalty. Medium armor has a 15-35% penalty to speed and a 5-15% penalty to evasion, plus a penalty to stealth. Heavy armor has a 45% penalty to speed and a 55% penalty to evasion.

What are the approximate resistance bonuses provided by light, heavy, and medium armor?

Light armor provides a small resistance bonus of 5-15%. Medium armor provides a resistance bonus of 25%, and some types block a fixed amount of damage. Heavy armor always blocks a fixed amount of damage, approximately 50, but it doesn't block damage completely; 2 points of damage will always get through.