On question 4, concerning the fate of the human species in terms of millions of years, this is the kind of question that contains so many of your own assumptions that I can't answer it on that level.
You are proposing questions from an inhuman perspective upon being human. In relationship to cosmic time, nothing matters. I am a human being, not the creator of the universe looking down upon all of time and creation. It's a question of scale. You are framing the question within a timescale within which human agency doesn't even exist. And then you are asking me to express my human will (my sense of agency) about what should be done. To me this is like arguing about how many angels fit on the head of a pin. It evokes a longing for God-like power and control over our fate that can never be satisfied, while annihilating the "zoomed in" realm of our own human-scale existence (our collective human subjectivity) in which we can meaningfully participate.
It also suggests a longing for humanity to have some kind of absolute, eternal value.
Can any human, even a scientist, actually does transcend their humanity, for even a second? Is the objective, third-person (out-of-self) perspective of science, which claims to be the unique truth, a scientific delusion? And in fact a shame at being human, vulnerable, and transient?
Finally, does that third-person, objectifying and aestheticizing perspective lead to the legitimation or rationalization of dehumanizing practices and treating people as objects, simply by treating their experience as unreal and off-the-books, externalized out of the system of thought, in the same way that mainstream economics excludes the lifeworld?
I'm thinking of how marginal groups are first dehumanized by the power structure, to prepare acceptance for violence against them.
So the question is, whether the objective point of view promoted by "scientism" lays the ground for violence or oppression of those objectified.
You have said that the Hubble perspective confers humility by showing that humans are mere accidents. That a human-centered perspective is narcissistic.
This brings up the issue of "man is the measure of all things" which is what you say is at the center of what you define as Humanism in the Anti-Humanist manifesto. I think the implications of whether to use a human scale -- in regards to your question 4 on the lifetimes of species -- could have a different relation to humility than you say.
There is an issue of humility in the perspective, and not just in what's being contemplated.