Excellent points!!!
Someone clearly must have provided substantial information as to how, when and where to enter the Sievers' home. Then, would JR be capable of doing this alone? Or, was WW also at the house, or in the neighborhood as a driver? Without advance information this perp or perps would have had to be extremely lucky to know all the details you mentioned. It seems unlikely that he or they were not prepared. I would say that if WW had not been charged with murder, it may have been plausible that WW intended to steal something important and JR became uncontrollable when faced with TS discovering them, but I don't believe he was charged as is unless he was a co-conspirator or the middle man. At this point I am not buying the robbery theory, I am believing the hit man theory.
Also, there's that bloody jumpsuit ... how can that be explained away? It almost proves it was a planned murder and not merely a robbery gone bad JMHO