If Elon really wants to look innovative smart and cool by advancing cybernetics why the fuck did he start with the part of the body that is crucial and will instantly kill you if something goes wrong?

Because he has zero patience for any of the practical steps of scientific progress and just wants the noise, spectacle, and above all else, the praise and worship of everyone possible.

the part of the body that is crucial and will instantly kill you

I think you answered your own question. He wants to play god and messing with the brain is more fun for him. And if he kills somebody and their family sues him for $100m - what does he care? He can spend literally millions on legal fees to drag the case out for years and years to try to break them. He gets to play god again.

If he wins - he’s on cloud nine. If it looks like he might lose - he can offer them a deal - the money with an NDA. Then he can have private detectives and tech bros follow them around for years and if they break the NDA - he’ll fuck with them by suing them.

I just made myself throw up in my mouth.

Listen if I can’t be turned into Jax from Mortal Kombat, then I’m just not gonna care.

Possibly part of his techbro fetishisation of immortality. Get the NPCs to crash test the implants and speed development, then something something, post-singularity godmind ruler of the internet (who the meatspace slaves all think is Really Cool because of their nerve staples).