Looking for feedback from people who created a smartphone app

Hello everyone!

I want to create an smartphone application that helps the user to adopt an healthy diet.

If you have created a smartphone application, or have general knowledge about it, I'd like to hear your feedback, especially on the following topics:
- How many people, including you, worked on the project? What were your roles?
- What is your business model? If your app serves as an intermediate to sell products from other companies, what percentage do you take on those transactions?
- Did you develop the application yourself, or did you hire someone to do it?
- If you developed it yourself, what language/technologies did you use? How do you connect to third-party systems?
- If you hired someone else, was it a freelance or a bigger company? What would you recommend?

Tank you in advance for your feedback!