Regarding Charles Manson and the murders of Sharon Tate, I have heard that the location of that murder was chosen because of past experience Charlie Manson has had at the house. He was one time visiting one of the Beach Boys (Dennis Wilson) who lived at that very house at one time. The article that I read said or speculated that Charlie Mansion chose that location because it was the house of Dennis Wilson and Charlie felt disrespected and betrayed by Dennis Wilson who originally met Manson, also a musician, through some of Manson's girls who were hitchhiking and Wilson picked them up. They in turn introduced Wilson to Manson who freaked out the other Wilson Brothers and members of the Beach Boys who counseled Dennis to get far away from Manson, which he did.
Charlie was incensed that Wilson would not have anything further to do with him and it's thought that Manson's anger, toward Wilson set up the visit to the house that was then occupied by Tate and her husband and friends. As for the markings on the wall and the other murders you are correct about his hopes to start a race war. He was one demented person beyond rehabilitation and California should have executed him long ago rather than house him and feed him all that time while the relatives of his victims had to further suffer knowing he continued to live while their relatives died.