There are a number of named minor characters in The Merchant of Venice who still serve a particular function in the play.

Lancelot Gobbo is the servant and clown of Shylocke who later ends up working for Bassanio. He serves as comic-relief throughout the play and also demonstrates just how unpleasant it is to live under Shylock's roof.

Solanio, Antonio's bigoted friend, often illustrates the rank antisemitism in the play.

The Duke of Venice's role is to represent the function of law. He fulfills his duty to the law even when it goes against his own preferences. The Duke also represents the notion of mercy when he urges Shylock to be merciful.

Prince Arragon of Spain, a self-absorbed elitist, has come to Venice win Portia's hand in marriage.

Prince of Morocco, always dressed in white, is another one of Portia's suitors. He urges Portia to ignore the color of his skin when considering him.

Balthazar is Portia's servant. When Portia disguises herself as a boy, she uses Balthazar's name.

Tubal is a wealthy Jewish merchant and friend of Shylock. He lends Shyock the 3000 ducats that end up as Shylock's loan to Antonio.

Gratiano, Bassiano's loud-mouth friend, serves as a comic, if somewhat obnoxious, minor character. He's an accomplice in the kidnapping of Jessica, falls in love with Nerissa, and is an enthusiastic witness at the trial.

Nerissa, Portia's lady-in-waiting, serves as her mistress' confidant, companion, and verbal sparring partner.

All the characters in the play are listed here:

http://www.enotes.com/merchant/list-characters

With their names, you get a one line summary of their role in the play. This includes the minor characters, and you can use this as a kind of checklist for your project.

A more detailed description of the characters is found here:

http://www.enotes.com/merchant/other-characters-descriptions

And finally, an analysis of the major characters is available as well. This would be Portia, Antonio, Shylock, and Bassanio.