I more or less agree with you on point 1. A rational person could have reasoned in that way. But I think we have to say that Light did not. He wanted people to recognize his work when it came to killing apparent criminals because he wanted admiration as a goal in itself. This led to the most obviously avoidable mistake, #3.
I disagree, even in the very first episode he specifically outlines that part of his plan is that when people notice criminals are dying they will be less inclined to become criminals.
I wouldn't say #3 was that easily avoidable, I didn't see it coming myself, while in #4 it was all I could do to restrain myself from yelling 'idiot!' at the screen.
I don't know if this is a little too afar field for even a Discussion post, but people seemed to enjoy my previous articles (Girl Scouts financial filings, video game console insurance, philosophy of identity/abortion, & prediction market fees), so...
I recently wrote up an idea that has been bouncing around my head ever since I watched Death Note years ago - can we quantify Light Yagami's mistakes? Which mistake was the greatest? How could one do better? We can shed some light on the matter by examining DN with... basic information theory.
Presented for LessWrong's consideration: Death Note & Anonymity.