5.In the vim editor when I open a file and type ':set list', i see a '$' at the end of each line, what character is that?

From :help list:

Same as :print, but display unprintable characters with '^' and put $ after the line. See |ex-flags| for flags.

So the $ is just an indicator for whatever vim currently consideres a newline (which is determined with :set fileformat).