I’m not sure I fully understand what you mean when you write about “an advanced stage in understanding Russian”. The definition is to some extent vague for me. In case you wish to reach the pinnacle of C2 level*, it’s possible, feasible but takes a tiny little bit of time and effort. Ten years of “hard labor” might be enough to reach the stage, though it’s just a ballpark figure, based on what I’ve seen in the net over the last three years. If you want just to read effortlessly in Russian, you probably can reach the goal for about 3+/-1 years, given you can force yourself to learn about 15-30 new words per day without breaks and periods of procrastination. As for teachers, I believe you don’t need them at all. Internet can provide you with everything you may need to know about the Russian language, and no tutor can expedite dramatically the learning progress.
*Common European Framework of Reference for Languages - Wikipedia, the free encyclopedia