That's also an option, förbereda sig på is used pretty often and the meaning is more or less the same. However, we want to minimize the things showing up in multiple choice questions that can be tricky, so I'll try to remove it as something that can show up there.
No, it sounds strange. The verb starta is used with things you control, that don't have agency. You would starta en motor, but things like school or a theatre play are considered to be more like things happening to you, and require börja instead.