How does Shakespeare discuss the themes of disguise in Twelfth Night?

Disguise is the key theme in Twelfth Night and this question therefore opens up a discussion with a lot of scope. Details about characters can be mentioned and it can also be linked to other themes. Starting with Viola, the obvious, due to her physical disguise of her gender, you can discuss her reasons for this. Is it because she would not be able to succeed in a world like Illyria as a woman. Is it because she is trying to stay connected to her brother who she assumes to be dead? Viola uses her disguise as a tool to deceive and this opens up a discussion to Olivia who is most predominantly deceived by Viola.
When discussing disguise it is crucial that comedy is mentioned. Twelfth Night is a comedy and therefore Shakespeare uses disguise in this sense to create humour. The deception of Olivia does create hilarity, she has fallen in love with a Women and pines for someone who is cross-dressed. Key quotations of this comedy need to be included in your answer and analysed to prove this point.
Be sure to also look into Feste and how disguise is not always comical. His taunting of Malvolio whilst he is disguised as Sir Topas the curate is unsettling and not light humoured. This is also an interested angle to explore when tackling the theme of disguise.