How quickly do you want to be wealthy?
I don't want it to be in a short time. Otherwise, easy come may easy go. A quick wealth might not be fortunate some of us.
What do you think is an appropriate amount of time to build that level of wealth?
I think 10-15 years enough. There should some time to stay that wealth.
How many people in the world have that kind of wealth?
I think it is the dream of many people. However, even if you retire with enough money, the problem is whether you will have energy and health to spend that wealth.
That is what happens to many people's earnings here :)
That is pretty reasonable to build a steady income stream I believe. It is like building a business, the first few years, everything goes back into development and growth - after that a small living wage comes out with more going back and then finally, it is a bit smoother, with a larger wage possible, but plenty staying into develop further.