Unless you are already really experienced with the different classes and their synergies I would probably recommend minimizing the number of classes you start out with. This will allow you to learn those classes really well in a group setting and it will also minimize the complexity of your multiboxing configuration because everyone (mostly) will be using the same abilities.

Once you are more comfortable with the classes (and with doing complex keymaps in ISBoxer) I'd introduce more complexity in your group composition.