1) The main difference is the North American version doesn't have Dark Aeons, Anima's Oblivion and the Magus Sisters' Delta Attack only hit once, and Quick Hit is cheaper to use. There may be more, but that's what I can recall.

3) You can use the same aeon against them, but generally it's better to keep your characters in battle. They are quite hard and will require extensive levelling up, unless you plan to Zanmato them.

5) It is possible to beat them when you have <10,000 HP. In fact, many players are of the opinion that BHPL is entirely unnecessary.