Who is this play really about?
I'm going to take the IB stance and claim that this play is not actually about any of the characters in the novel, but rather who they represent. Each of the major characters seems to be a manifestation of stereotypes of the day. Solarino (the stead-fast anti-semetic...nearly everyone at that time), Shylock (the greedy Jew), and Anotnio (the minority of the population who has seen the error in their anti-semeticism and realize that Jews are people too). This play is not about these characters. It is a portrayal of the world as it is and the societal conflicts that are arising as Europe is begining to shift away from this anti-semeticism.
Is Portia the "poor little rich girl" or the cunning imposter who saves her friends,
I think that in a way Portia is the "poor little rich girl" but her actions convey that she is trying to rid herself of that image. In the beginning of the play when she and Nerissa are discussing the lottery, Portia complains of her situation -- when in fact she has no reason of such complaints. Initially, she conveys herself as a "spoiled brat" -- but after involving herself in the trial of Antonio and demonstrating her intelligence and bravery, I know believe she is more than a "poor little rich girl". She's more of a.."poor & smart rich girl" ;) .
1.> Who is this play really about? Shylock? Antonio? Bassanio? Portia? Jessica?
I think this play is centered around religous prejudice. All of the main characters are in some way, "bound" to Shylock -- either directly or indirectly....making Shylock the object to which around the play revolves.
Risk, Bond, Exchange, Love
This is play, all these concepts (risk, bond, exchange, and love) are important because, first of all, the play starts with risk and ends with risk. In the beginning, Antonio risks his money on his ships and the sea. After that, Antonio risks his flesh in exchange for Bassanio and his love in a bond with Shylock. At the end of the novel, Antonio makes Bassanio exchange his ring with the lawyer for his "fees," which risks Bassanio's promise with Portia. Portia saves Antonio during the trial for her love for Bassanio. Shylock loses everything he had for a bond that was not clear enough to punish Antonio for not being able to pay him back.