I think that much of this is going to be dependent on what you have to prove in your thesis as well as what you particularly feel about Kushner's work. This might require you to take a step back and ask what you felt was the most compelling or thought provoking argument to come out of the work. In doing so, I would suggest that assessing how Kushner's work takes the ideas of identity, the American Dream, as well as personal growth and applies it to gay and heterosexual individuals is something that you might want to consider. Kushner's real talent is that he allows the reader to cross a threshold (perhaps, a "threshold of revelation") where the despair and agony felt by his characters cuts through sexual orientation borders. While the work is seen as a landmark in LGBT literature, it should not be overstated to the point where the work reflects all of the same issues in both gay and straight characters. I think that your essay could pick on any of the themes in the novel and argue how these are relevant to both gay and straight characters in Kushner's work.