How should I structure exams when individual problems could use up the entire class time?
The most time-consuming and least information-bearing step (at least for the purpose of evaluating understanding of the material) is 4. In this situation I've often just given questions asking the students to do 1-3 and explicitly told them to not go through the calculation. It's better if you prep them for this by giving such a question on a quiz first since many students tend to go on autopilot after a couple of decades of being trained to come up with an answer.