Im a native Macedonian (slavic) speaker and all I did to have my 1st successful conversation, with a Russian speaker 2 days ago in Russian ,is i finished all the Duolingo lessons about Russian.
When you say im gonna learn Russian you should say im gonna learn "Slavic".
Russian is easy for me because is 80% the same words, its preaty cool. So please learn Russian, if you ask me , it is a easy language.
After learning Russian, you will understand Ukranian and 70-80 % balkan slavic.
If you say one sentence in 3 languages (Macedonian, Russian , and Polish) all 450 million slavic people will understand you