[SwissXC90]

To put this into perspective.

I have developed software to analyse and program devices on BMWs and recently applied that to Volvos.
Here’s my practical feedback:

You go nowhere very fast without an emulator and test environment right next to your main pc that you program on
You need experience. I had 20 years of it. Without it the development time takes orders of magnitude longer
You will experience unforeseen show stopping hurdles that will cause rethink and redesign
You will spend every waking minute on the project for over a year

And that was my personal experience.
It can be done.
It is by no means easy
You need a solid idea and structure. Both in your head and your code.