(1) Geomantics is a parapsychological study of land/house, just like fortune telling to human. Geomantics is just like a arabic/persian divination edition of Chinese I-Ching.

Actually, Chinese FengSui was translated as geomancy before, before FengSui was widely studied by western world at recent decades. FengSui to western world is just like a Wa-Se-E-Go in Japan.
(2)Yes, things will be different at southern hemisphere because your interaction with sun, moon, astros and environment (Yin-Yang-Wu-Shin) and people are very different.
(3)ZiWei and BaZi is somewhat accurate if you are an "average" individual, like people born at HK/TWN/CN/VN, and live/work/marry there. If you live/travel around the world your providencial chart probably no longer applicable.
That is why many criminals escape abroad and their life trek and chart reset allover...
That is why people's face and palm change. I notice my and my wife face changed slowly...