Do you know any advices how I can overcome this terrible SI And finally free myself from all my sadness, emptiness and suffering? I think I'll have one drink before I hang myself fully. Do you think that will work? I don't want to make myself drunk because then its too risky that I could do something wrong. but is there maybe something else I could do? Some mentioned that they wrote a list about all their reasons do it.
How to overcome SI? If I knew the answer, I wouldn't be able to tell you.

I stole this from someone. Might have been
@Gustav Hartmann who said it, I'm not sure. The point is that people talk, but no one who's alive
really knows, because if they actually knew, they'd be dead already.
Writing down a list of reasons is a good idea, and it's something I've done myself.
I made a post about it a while back.
I'm not sure if alcohol is a good idea. I plan to do it sober. Partly out of principle, and partly because alcohol increases the chance of making a mistake. But if I'm unable to go through with it, I might try taking a couple of shots on my second try. I agree that doing it fully drunk is risky, and I wouldn't do that either.
There is research (
1,
2) that shows that about 30-35% of suicide victims have a positive blood alcohol level at the time of death. Percentage rates vary, depending on method used and some other factors. So a lot of people do it sober.
Other than that, just the usual stuff. My plan is to be fully prepared, practice everything, and do 'trial runs' to familiarise myself with the steps and the process. At the time of my actual attempt I should be able to go through the motions mechanically. My plan is to simply not think and shut out any thoughts. That's my 'method'. I believe we can't reason ourselves into doing it. There isn't a state of mind where we can be at peace with it and where it becomes easy or even doable. My solution will be to not think and just do it.
I also want to be well rested. When we're tired, it's difficult to do anything or make hard decisions, and our willpower is low. I'll have nothing planned for the last day, just rest, and maybe some very simple activities to pass the time, like listening to music or watch something. No decisions, no thinking, no major tasks for the last day – those should have already been done by then. I'll just relax, do nothing, and go through the plan.