I'll try to answer your questions.
A1. When King Grayskull died he transferred his essence into the Sword, so now it contained both He-Ro's Cosmic power and KG's power. The magic was drained from the Sword after KG's death (by the Elders/Veena) and became the Orb (changing the Sword's colour from translucent blue to grey in the process). Eventually the Elders added their power to the Orb as well.
Castle Grayskull must contain other sources of magic, because the Sorceress does not draw upon the Orb for her magical abilites.
A2. I'm not keen on the idea that the Power Sword can be cloned or duplicated either. Since the prophecy speaks of twin warriors, there should have been twin swords created at the very start.
A3. I think so. We still need confirmation of that.
In addition to the Techno vest, Prince Adam also used the 200X sword until he found the Sword halves.
Oh, and He-Ro was a Cosmic Warrior, not a Cosmic Enforcer. He battled against evil, while Enforcers like Zodac take a more neutral stance.