So the answer is quite trivial, but since I spent several hours to reach it, it might save some time for others-
- Download & install STS IDE.
- Import the project as existing Maven project.
- Run/Debug the project.
I tried to run it via Eclipse the whole time (wasn't familiar with STS to be honest) and this probably needs some extra configuration (another comment with explanations on eclipse configuration will be much appreciated). Once you work with STS, it's easy.