In my locale, the only thing that matters is passing the code inspection. I have friends who have done major remodels, including additions. The piece of advice

In my locale, the only thing that matters is passing the code inspection. I have friends who have done major remodels, including additions. The piece of advice I got was to talk with your inspector before starting. In my city, they have office hours and will help people avoid surprises such as finishing the interior walls before having the electricals inspected -- stuff like that.