C-note, from the Roman numeral C for 100, although this usage is far less common today than it was in the early 20th century.
Not sure, maybe comes from the sound of FIVE.
The term derives from the fact that older versions of the bill included the roman numeral for ten; which resembles one of the ends of the wood supporting device described above. This name was most common in the days of large-sized notes. In poker terminology, [sawski]; refers to a sawbuck.
I do not know.
Sorry! I am unable to answer all of your questions, I hope someone can help you about that.