React Native app not running in XCode iOS simulator

I try to make my first steps using React Native. Development for Android (on Windows host) works. Now I wanted to test iOS, and tried to set up a development environment on a MacBook Pro.

Problem: React Native starts the iOS simulator, and then nothing happens any more. The simulator runs OK, but my React native app won't start.

What do I need to do to get my React Native installation going?

More Info:

I set up XCode and React Native according to the docs on the MacBook Pro running OSx 10.13.2 (High Sierra). XCode was installed and tested successfully, including the simulator.

When I installed Node.js I deliberately picked an older version (containing npm 4.2.0), since forums say that React Native does still have problems with npm 5. I also installed Homebrew and Watchman, like stated in the docs.

To initialize an empty project, I used

create-react-native-app HelloWorldProject

and a projet structure got created in my Documents folder.

If I finally fire up my "Hello World" test app using

cd HelloWorldProjectsudo react-native run-ios

the system responds:

Starting packager ...Starting simulator ...

and then nothing happens. The simulator does indeed start (boot --> apple logo --> progress bar --> IOs start screen), but nothing happens afterwards.

EditI have given up on React Native for several reasons, I leave this question here for documentary purposes, but I cannot verify or accept any answer, I don't have a React Native development environment any more.