I'm a an app developer from Germany myself and having built 31 apps over the last 3 years, some with more than half a million downloads, this app should be pretty simple to build.

If the questions are stored on the device, I can build this app for iPhone (native) for $1,300 for you if you want. If the questions come from the backend, I could build it for $1,900 for around $2,400 if you want to add push-notifications to your app.

We can set up a call and I can help you with the requirements of your app.