How does Shakespeare use his characters to represent the various type of people in his audience?What characters would amuse those in the audience...

Shakespeare's plays were popular with all classes during
his day, which accounts for his success as a businessman (part owner of his theatre
company) and as a writer.  It would be hard, I think to say which class was amused by
what, rather safer to acknowledge that the humor was enjoyed by
all.

That said, Shakespeare did include, even in his
tragedies, characters whose job in the play was to "be funny."  Certainly Bottom serves
the purpose in A Midsummer Night's
Dream.

But who was amused by him?  Well, first
of all, the actors would have been.   Bottom lampoons the sort of actor everyone who's
worked in the theatre knows -- the diva.  He's the actor who wants to tell all the other
actors how to play their parts and thinks he could do them all better than anyone else. 
He's the actor who milks all of his lines and stage time (notice for example, how many
times he says that he dies as Pyramus in Act V).  So, even today, actors and theatre
people everywhere, get this humor.

But he's not only an
actor, he's a bumpkin.  All of Bottom's fellows come from the working class, and, as
such, are ignorant of how exactly to put on a play.  Shakespeare makes fun of these
simple hard-working fellows, and probably all classes found this funny, even those who
saw themselves in the "rude mechanicals."  The actors playing these parts would have
been adept at these "clown" characters, and audiences probably recognized their favorite
actors, who tended to play the same type parts over and
over.

As for superstition, it was a part and parcel of 16th
century life, so it is also safe to assume that all of Shakespeare's audience was
superstitious.  Unlike a play like Macbeth, however,
Midsummer doesn't really trade in superstition, more the fantasy
and magical aspects of the supernatural.  By setting all the supernatural events in the
forest and casting the dreamlike quality over everything, there isn't anything ominous
here to cause alarm in someone who was
superstitious.

Lighthearted, magical happenings and poking
fun at actors are two aspects of A Midsummer Night's Dream that
would have amused audiences in Shakespeare's theater.