Guide to Core-Contribution

Hello guys,

I am a Web-Developer, but have just some basic Understanding of PHP.
Wordpress is my big love and I would like to help improving it, by contributing to the Core and being able to tweak and customize everything about WordPress, so I can use it to cater to my and my customers every need.

So what would be the best roadmap to become a WordPress-Guru and Core-Contributor? I searched for Courses, but I couldn´t find any that help you getting that deep into WordPress. Only Beginner-Courses and “How to make Money using WordPress”.

It would be awesome to get some suggestions from you guys.

Greetings,
Marvin