Happy to hear that you've enjoyed reading my books. My answers to your Questions below:
1. You've mixed "Eight Mansions" with "Annual Flying Stars" system and tried to read them together. They are both different systems. Hence your confusion. While both are valid systems of Feng Shui, their 'stars' don't counter each other. Think of it as AM and FM radio. Both frequency exists at the same time, but they do not clash. And no, the Fire Star does not destroy the metal sector. It merely enters the West and it's energy will interact with the West's metal energy. In any given sector, all 5 elements exits at the same time. It's a question of which element is stronger and how it affects the occupants.
2. I think you are trying to forcefully combine the Eight Mansions ONTO the Flying Stars sytem, trying to merge-read the two systems. They are independent techniques. Both can be applied together, but on different layers. In fact, when you move deeper into feng shui, there are yet many more layers - like Dragon Gate Eight Formations, San Yuan and San He techniques. If you try to 'merge' them, you will be confused. See them as layers - much like layers of clothing of a person. They reveal to you different aspects of home.
Hope this helps.
Warm Regards, JY