Good progress here Razvan :).
I think you're on the right track with focussing on the fundamentals. Remember that 80% of your progress can be achieved by focussing on just the right 20% of the skills.
The right 20% being the fundamentals: perspective, lighting and colour.
Practicing construction in perspective using primitive forms is a great way to get better at perspective and lighting.
Another principle that I find very helpful is to focus on the process instead of the result. If you become good at executing the right process, then the result will take care of itself.
You're also being smart by following the teachings of artists who have mastered the areas you want to conquer. Finding good teachers will point you down the most effective learning paths.
Check out this link on effective learning, I found it most helpful:
http://www.lifehack.org/381775/5-powerfu...ing-faster
Anyway, hope this was helpful, if not, please ignore :).