The limits of planning in any kind of conflict have been described by a number of military theorists as something like: No plan survives first contact with the enemy. Mike Tyson, the boxer, put it this way:
“Everybody has plans until they get hit for the first time”.
So BK could have done all sorts of planning--from what to do with his cell phone to his routes for getting to the house and escaping the crime scene--that has turned out to be not very smart. But no matter how many scenarios he ran in his head as he planned and envisioned the attacks, his plans were almost certainly not going to describe the real life situation of multiple murder in small spaces, with actual humans who in some cases could fight back and make noise, with a dog that started barking and probably disrupted his mental time line. Even if his plan seemed flawless to him on paper, it would not have survived the reality of murdering four people. My opinion only, of course.