From what I've heard about Asian BB creams, they have more pigmentation. Meaning they are like a foundation.
1: Primer can help smooth out the the surface of your skin before applying more makeup. BB Creams are supposed to smooth skin and provide some coverage.
2: You shouldn't need to wear both foundation and concealer if you are wearing BB cream. If the BB cream doesn't cover enough, add concealer where it's needed. Otherwise, fuller coverage foundation and concealer might be a better option.
3: This I don't know. I would read up on reviews of how long BB creams last on other people. Some of them may last 6-8 hours or more. A makeup primer should extend the wear of foundation and concealer. If it doesn't, the products are incompatible.
4: I don't understand this question. No one has to wear anything. If you choose not to wear a BB cream, that's fine. Unless you are allergic or sensitive to the products you choose, you can choose to wear (or not wear) any makeup on any particular day.
6: It depends on the techniques and the amount of coverage each product gives. Typically the routine is: primer, foundation/BB cream, concealer, powder. At least, this is the routine I use. There are lots of videos on YouTube on creating flawless skin. They can give you ideas.
7: Between which two things? BB Cream and foundation?
If your skin looks very pale in photos, you may be using products with SPF (sun protection), or simply the wrong color. Or you can blend the product into your neck and onto your ears. This way, your skin will look more even toned.
Here is a link to videos about BB creams
, including reviews, application techniques, etc.
Hopefully some of my rambling helps!