So I assume you have a table of professionals, and each professional is tied to a ZIP code? If you haven’t done that, you can structure your table to be like that, and the search in a collection would be enough to show the corresponding professionals.
This would be collected in an onboarding process.
Do you mean you want to monetize the app? What features do you think people would pay to use? Do you plan to have a freemium model or something else?