Osmand doesn't appear to be able to locate street addresses. Like if I input something like "123 4th Street" all it can do is offer some cross streets, which may be miles away from my intended location.
Is there a way to augment it's data so street addresses work? Maybe there's a service I can add?
Similarly, it doesn't know the names of many businesses.
You can add missing data by yourself. Start with StreetComplete app for address numbers and https://www.onosm.org/ for businesses. If you want to go deeper check https://learnosm.org/en/