Its not a ruler. During the draft, you can use it to track gold totals by placing a die (or dice) next to the correct count.

Mechanically, no, but we wanted a distinction for thematic reasons. Some cards, such as Thorn Elemental, do interact differently with each keyword.

Yes. Note that you cannot use the ability in-between movement points. For example, if a unit with Movement 2 uses a combinable ability, it cannot move 1 hex, use the ability, and then move another hex.

No. Ranged units always attack from range and will never take over the defender’s hex if they kill the defender.

Shields are a form of damage reduction. Pure damage ignores all damage reduction effects. When unit receives pure damage, you would deal that much damage to the unit and, if it is still alive, it will have the same amount of shield that it had before combat started.

No, except for heroes and units with the Legendary keyword. Only one hero can exist in a kingdom and only one copy of a Legendary unit can exist in a kingdom.

Yes, but it would just be a waste of gold since no abilities have effects that stack.

No. Ability levels are not considered part of the ability name. Therefore, Quicken 1 and Quicken 2 are both considered the same ability and the “Use this ability only once per round” restriction applies.

No. See this section of the Basic Rules to understand how modifiers work.