Question: Did Stalin and Lenin have beef? If so, what about? Did Stalin really betray Lenin's ideas or is that not true? Please support your answers with evidence, quotes with sources, official documents, information on policies they endorsed (separately and/or together), etc. I'm trying to formulate my own position on this.
The TLDR version of this history;
Lenin and Stalin were colleagues, and there's not much that actually supports any sort of "beef". The thing that's usually used is this letter, wherein Lenin complains about Stalin. There is reason to believe that the letter is faked by devious actors, but even if it is real, it just reads as venting. Taking "Lenin hated Stalin!" from the letter is like assuming best friends secretly hate each other because one of them made a post while upset on social media.
Stalin was a staunch supporter of Leninism, and stayed true to Lenin's ideals of the Soviet Union while expanding the theory to fit the geopolitical situations that unfolded under Stalin's time as chairman. Foundations of Leninism is a summary of Leninism written by Stalin himself, who wasn't much of a writer.
The whole thing seems to be propaganda by Trots and Anti-Communists to pose Stalin as an evil dictator who illegally took power of the Soviet Union for his own benefit, against the will of Lenin. But the reality is Stalin was democratically elected into this position and staunchly upheld Marxism-Leninism and led projects that benefitted the entire Union and her people. Stalin is a beloved figure by not just Russians and Communists in the western-sphere, but by people in every corner of the world for good reason.