5. I hear a lot of people using amongst instead of among. What's the difference?
There is no difference, and we hear either word in speech. I suspect those who use amongst are trying too hard to speak properly. Or they're trying to sound British, among whom the use is common.
The use of amongst hasn't aged as badly as whilst, but they both come out of the same period. For consistency, if the speakers (or writers) use amongst, I would expect them to use whilst. Strange, but I don't hear the second word.
Along the same line is the use of as to, which I read and hear often these days. As one grammarian told me, "As to is a stuffy substitute for about." The prosecutor asked him about his action (not as to his actions).