Pardon this first question:  I think that the FAQ "rules" said not to
ask about Google or Answers, but somehow I can't believe it really
means not simple USAGE questions that do not seem to be supplied
elsewhere.  So here is possibly a wasted 50 cents.. . . . .
Is there a way to sort existing "open" questions to identify those
with the most comments (decending sort)? if not, perhaps, why not? And
is there a way to see and sort (by price or date) existing "answered"
questions and then "buy" an already researched answer and/or the
comments related to it?  if not, perhaps, why not?

I don't know of any way to sort questions by number of comments.
Regarding "buying" an already researched answer, all answers and
comments are posted for everyone to see, and no further payment is
expected. If you like a certain Google Answers Researcher's work, you
can post a new question directed at that Researcher. It's always
flattering to be asked for by name.