I want to learn mobile programming by creating an android health application, where:

1. user could use the application to order every kind of vaccine that they wanted

2. then they accept or decline the agreements that existed such as they are in a healthy condition, no refund, etc

3. they pay the vaccine using credit cards

4. the nurse came to the user house to give the vaccine

In chegg's experts opinion, what is:

1) the best yet easier tools and technology from third parties (cloud services, API services, etc) and the use of sensors on the device?

2) the opportunities and challenges of the application

*Please give me detailed explanation of your answers, I wanted to learn from you. thank you very much.