Restoring an old Vespa, how do you start?

Good evening everyone,

As I've already described, I'd like to restore an old Vespa with my father (a car mechanic) and then ride it together. However, the topic is incredibly broad and not easy to grasp. Does anyone have any tips on how to best get into it? Which model is most suitable (among the 50s models)? What should I look for when buying? What else should I consider? Are there any guides or forums for this? I would be very grateful for any tips!