In Act I Scene I, what are the methods Shakespeare uses to spark the audience's interest?What is the atmosphere in the scene?

Your question had many sub-questions in it, so I will
answer your query about the atmosphere and the methods Shakespeare uses to achieve
it.

The play itself doesn't really create atmosphere.  The
setting, characters and action implied by the characters' words give a good foundation
upon which to build a plan for creating atmosphere, but  the atmosphere itself is a
purely theatrical construct and must be created by those who produce the
play.

In Shakespeare's day, they would have had some
impressive (for the day) special effects for thunder and disappearing/reappearing by way
of trap door -- all of which could be utilized to set a rather ominous, spooky and
other-worldly atmosphere for the opening of the play.  Lighting of any kind was not an
effect in the open-air performances of The Globe, so the audience and actors would all
have remained in the afternoon sun that lit the
performance.

The appearance of the witches to open the play
would have definitely sparked the audience's interest in Shakespeare's day.  In the same
way that we, today, have audiences who are fascinated with vampires (think
Twilight), Shakespeare's audiences were fascinated and repelled by
witches.  In fact, there were witch hunts still going on in Europe at this time, and
ordinary citizens believed that a witch might cast a spell on you if she did not like
you or you offended her in some way.

So, all of the witches
talk in spell-casting rhyme,  their talking about their familiars (animal sidekicks),
etc. would have really caught the interest of Shakespeare's audience.  Add to this the
special theatrical effects and the atmosphere would have been ominous, creepy and
supernatural.