1) Correct, Tech power only applies to Tech attacks.
2) Tech attacks never use AmountModifierPercent or Weapon Damage. They may have a AmountModifierPercent value, and it's often 0.01, but it's not used.
3) A good way to check to see if you're getting it right is to see if you can calculate your tooltip values. When you can get those 100% accurate you can then apply damage reduction from armor, expertise, etc.
4) Abilities from the skill trees use your characters level for the lookup table.
There was a bug, not sure if it's still in effect, that caused the tooltips of those attacks to use the level the ability becomes available, but the actual damage used the correct level. So you if you calculate the damage of these attacks you may find them doing more damage than the tooltip indicates.
Thanks for the clarifications! That helps my calculations out a lot.