If we have the choice to study Hawza part time (to aquire essential knowledge that we need) while being satisfied with a career with more monotonic and not so rewarding work or a more rewarding career with more income and maybe building family also while studying on ones own some islamic knowledge – which one would be best to choose?

You do not need to leave your job to learn the necessary rulings of religion, you can learn them from the scholars in your area, and thus maintain your standard of living, and be satiated in terms of religious knowledge