It depends on the question.
In my experience, I've used 3 artists in my Section II responses until I hit Year 12, upon which I used 4 artists. There isn't a limit or a magic number, but according to my teacher and friends in the older years, it's much more difficult to gain a higher mark with 2/3 artists than it is with 4. You'll need to go into a lot more detail, and honestly, it's not worth the aggravation and pain.
There is a chance that you might lose marks if you don't fully address the question. It's a first step that the artworks you plan to use are from different periods so that you can contrast the societal context and artistic techniques, but it's a good idea to choose a breadth of artists/artworks so that you're able to tackle any question thrown at you. Before the exams, I prepared around 8 artists which covered Dada, Surrealism, Pop Art, and Postmodern Art, and included sculptures, readymades, paintings, and screenprints.
I understand your inclination to one particular medium of art, but if you can pull it off, writing about a wide variety of art movements, artists, and mediums will really show the marker that you have a great grasp on art history. But above anything else, make sure the examples you choose are relevant to the question!
