What are the theatrical implications of cross-dressing in As You Like It?How do the ideas of transvestism,cross-dressing, and male characters...

Theatrically speaking, it was a convention of theatre in
Elizabethan England for young boys or young men to play the female roles.  Because
Shakespeare's company was an ensemble of actors who appeared in each of his plays,
actors generally were cast in the same sorts of roles over and over again.  For example,
one actor specialized in playing the fools, one was most often the leading man, and
there were particular actors who specialized in playing the female
characters.

This practice was not perceived as
"tranvestism" in Shakesperae's day.  This is a 20th century concept and is meant to
describe something of the sexual proclivities of the person doing the cross-dressing. 
For the actors in Elizabethan theatre, being a man playing a woman was simply the
theatrical convention, probably not meant as a sexual statement at all.  Audiences were
quite used to this and didn't associate anything odd or out of character or necessarily
sexual about it.

The fact that Shakespeare often gives very
masculine character traits to his feminine characters (Lady Macbeth, Cleopatra, even
Juliet), could definitely, however, be attributed to his complete awareness of the irony
of a man pretending to be a woman onstage, and having some of his female characters
decide to dress as a boy probably also satisfied his sense of theatrical
irony.

Shakespeare used lots of techniques --  including a
play within a play, direct reference to how "all the world's a stage" in the text of his
plays, and having female characters (already played by boys) decide to go undercover
dressed as a boy -- to remind the audience that the world of the play was purely
theatrical and not in any way "real," though it's themes and events might hold a mirror
up to nature.

So, the most immediate implication of the
cross-dressing required of some of the female leads in Shakespeare's comedies is the
theatrical irony of calling attention to the fact that there is really no "girl" at all
onstage, and that the world of the play is completely theatrical and in no way real at
all.

The British theatre company Cheek By Jowl became
famous a few years ago for an all male staging of this play which they toured in Europe
and the US.  Seeing an actual all-male production of this play might give you the best
information about the theatrical implications of cross-dressing in As You Like
It.