I would like to address the last paragraph.

As I see it, by "cogito, ergo sum," Descartes is saying something logical, not causal. Let me demonstrate: you can say that a function is differentiable, and therefore, it is continuuous. That is a logical statement, that comes from the defintion of differentiability - you can conclude continuity from differentiability.
And you can say that you ate, and therefore, you are full. This is not logically sound, since eating does not always fill oyu up, but it is a valid description of a process: you ate, and as a result of that, you became full.

Therefore, Descartes doesn't necessarily mean that his existence comes as a result of his consciousness, but the other way around: because he is conscious, he knows he exists, since had he not existed, he wouldn't be conscious.

need I say more