How do I download maps for the entire USA, down to the street level for offline use?
See this article for more information on how to do download a country / region, please check this article: How do I download maps for offline use?
Once you have downloaded everything you wanted, restart Maps Pro and choose "Vector map" in "Map Styles".
Downloading data this way will allow you to browse the map, search for streets, display Points of Interest and get directions. Check out this article that explains how street search works while offline: How do I search for an address when offline?