There will surely be some one more qualified than I to answer, and seeing how Im stuck on mobile, I wont be able to find you any links atm. Im not sure if he killed multiple people that were close with him but I know he ordered the kill on Trotsky. Trotsky and Stalin were basically competing to succeed Lenin and eventually Stalin was chosen to take over the role. So they were close and worked together under Lenin. Trotsky was pretty intelligent and wrote a lot about his intepretation of Marxism. His ideas conflicted with Stalin's and eventually fled to Mexico. Trotsky continued writing and gained a significant amount of support, apparently this threatened Stalin because he ordered the hit on him.

Sorry for how broad the information is, seeing how no one else has commented I thought I'd give it a shot.

Somewhat fair. One of Stalin's strategies for maintaining power was through executions, yes. He got his first taste of this strategy, so far as I can tell, when he was sent by the Party to Tsaritsyn (renamed to Stalingrad in 1925 and Volgograd in 1961). He advocated a policy of mass terror against the population - and partly if not fully implemented it - during the civil war, which he was later removed from only because of his poor handling of the military situation.

He later advocated its use - successfully - in the Red Terror during the Civil War. However, unlike his advocacy of violence and terror as a means to force submission against the population, his use of executions within the party didn't start until the mid- to late-thirties. Prior to this, his primary strategy was through exiling oppositionists and threats, possibly to menial party/state posts in remote sectors of the country, and through expulsion from the party as well. It wasn't until later that purging actually took on the meaning of bloodshed.

For example, take the Ryutin Affair. One of the last power struggles prior to this bloodshed was against Bukharin and Rykov. Martemyan Ryutin was a supporter of the two when they both were demoted in 1930. He was demoted as well, expelled, arrested, but then allowed to rejoin the party. He published in secret an anti-Stalin platform that was circulated around oppositionists, caught and sentenced to 10 years in prison. During this time Stalin reportedly advocated for Ryutin to be shot, but other Politburo members disagreed.

It wasn't until the Great Purge commenced following the Moscow Trials in 1936 that this policy of submission through terror was directed inward at the bureaucracy. Specifically this also included those with whom he had formally allied in bids to consolidate his power. Later in life he had a regular strategy of questioning, threatening and "purging" his central committee to keep them obedient - this included the threat of execution but was not limited to it.

For example, he made Molotov divorce his wife, after which she was expelled from the party (a vote Molotov abstained from but soon thereafter in a letter to the Politburo admitted his "mistake" and said he should have voted to support it). The next day she was arrested and exiled to Siberia where she remained until after Stalin's death. Molotov was demoted.

Good readings on this subject would be Khlevniuk's books Stalin: New Biography of a Dictator and Cold Peace: Stalin and the Soviet Ruling Circle 1945-1953 as well as Fitzpatrick's Everyday Stalinism which if I remember correctly discussed how the Terror trickled down through the population as a whole.