In most of the US (by population density) you are not allowed to do that type of work without a permit and permits would not be allowed to be open for 7 years. You would not be allowed to move into a house of any part of it did not meet current code, so the entire exterior would have to be complete, with insulation and insulation must be covered and every room must have so many outlets and so on that effectively almost everything except baseboards and casing needs to be complete before you could move in even to part of it. Hard to save money if you have to pay for two homes and permit renewals for years.

You would need to get a certificate of occupancy, yes. You would also need permits for some unfinished work, too.

You brought up the exterior needs to be finished. Do you expect to move in with just the frame? It seems fair to me to have requirements of basic livability and safety.

You could move in with things like some of the bathrooms unfinished, a kitchen unfinished if you have a kitchenette elsewhere, extra bedrooms unfinished, etc.