Woah! Hang on there just one second! Remember you can only ask ONE question, and you seem to have cunningly asked about 17 in one go! So in my response I am going to focus on confused gender roles. Look at how I answer the question, and that should hopefully help you to explain other themes in a similar way. Remember to look for evidence from the whole text.
Clearly with its cross-dressing and disguises, gender comes to the forefront when thinking of this play. Viola is the central character who disguises her self as a man, leading to all sorts of messy situations with no conceivable remedy: Viola falls in love with Orsino but obviously cannot tell him without revealing her disguise, especially as he seems besotted with Olivia. Olivia then falls in love with Caesario who is actually Viola. Shakespeare appears to be deliberately blurring sexual boundaries: Olivia falls in love with a woman, even though she is disguised as a man, and ironically Orsino often comments on Caesario's beauty, suggesting that he feels strongly attracted to her (him) even before he knows her true identity:
Is not more smooth and rubious; thy small pipe
Is all the maiden's organ, shrill and sound,
And all is semblative a woman's part.
This theme of homoeroticism is voiced overtly in the character of Antonio, who is clearly in love with Sebastian. Key to focus on however, is that the ending "excludes" Antonio, whose desires cannot be satisfied, whilst the main characters all happily settle down to "normal" heterosexual relationships after the resolution of the plot.
However, some critics reject the "neatness" of the ending and actually point towards a somewhat confused resolution of this gender blurring. This is particularly seen in the relationship between Viola and Orsino. Note how in his protestations of love, Orsino seems to want to prolong Viola's male disguise. Although he knows that Caesario is actually Viola, Orsino says:
Boy, thou hast said to me a thousand times
Thou never should’st love woman like to me.
Later on in his final lines of the play, Orsino states:
For so you shall be while you are a man;
But when in other habits you are seen,
Orsino’s mistress, and his fancy’s queen.
This stressing (and favouring?) of Caesario's identity even when the disguise has been exposed raises serious suggestions about which person Orsino loves more - is he actually in love with Caesario or Viola?