I don't think it's creepy. And I don't think it's weird to want to have someone present or even document it. Just my opinion.
You can sign documents stating this was your own choice and no-one influenced your decision or aided you in executing your suicide. Maybe a good thing to do even if you decide to do it by yourself. Whether this is legal or not will depend on the country you're in. I know how such a document would be called in my language but I don't know if there's even a concept for something like that in English. Anyway, I expect that @LetzteAusfahrt has taken this into consideration.
And by the way, no stress about expectations.This is not something where you have to take expectations into account. It's all about you @LetzteAusfahrt.
Yes, I imagined TheLastExit (in German) would write a letter in which he absolves the potential observer from any responsibility.
But I also understand how difficult it may be to find such a person willing to witness another's suicide.
Even if you pay him well (and I somehow think Letzte is expecting the observer to participate for a "scientific bliss"), it is hard to find a serious and reliable person who can be trusted not to back out at some point.
It is a difficult task, no wonder he is having problems securing an observer and a partner (if both are still part of the plan).
I also get how our friend is a perfectionist and wants to provide some purpose to his departure, but in all honesty - what novel information, not already known, can be provided from documenting the process of dying from SN?
We have photos, we have testimonies up to the point of losing consciousness, even if there is an observer - he cannot feel or see what a dying person is going through on the inside.
Yes, the idea and the plan are noble, and I really wish Letzte gets his last wish granted... but I think his last bits of consciousness at that moment of departure will be overwhelmed by the realization that his soul is not fading into nothingness, as he thought it would, but rather... feeling the effects of his brain secreting DMT, meeting with angelical entities and some long gone relatives, having to go through the retrospective of his life and the terms of his final act...
Just kidding.

Too bad Letzte won't be able to let us know what we all wish to know the most... the eternal question - is it nothingness, or... a new cycle?
He will find out at last... while we'll still be in the dark, with only his earthly opinion available to us in his thread "don't be afraid of death".
Do not go gentle into that good night... old age should rave and burn at close of day... rage, rage against the dying of the light.