Learn English – Is it correct to use “most” + “-est” together

It's perfectly fine. Let's rewrite it to see what's going on.

Original:

You're in a box on wheels hurtling along several times faster than evolution could possibly have prepared you to go.

"box on wheels" => "car"
"hurtling along" => "going"

Creates:

You're in a car going several times faster than evolution could possibly have prepared you to go.

Now we can erase this unnecessary part:

You're in a car going several times faster than evolution could possibly have prepared you to go.

Finally creating:

You're in a car going faster than evolution could possibly have prepared you to go.

If you want to go even further, you can simplify all this to:

You're going faster than you are prepared to go.

Seems all fine here!

No, that "for which" is wrong." At a minimum, it should be "for which reason."

However, it's better to have it changed, e.g., to:

As presented during the seminar, the development of public health terminologies and classification is of prime importance to us. This is why it is necessary that we all collaborate towards our collective mission to make a difference in the lives of people of the world.

or:

As presented during the seminar, the development of public health terminologies and classification is of prime importance to us. This is why it is necessary that we all collaborate towards our collective mission of making a difference in the lives of people of the world.

I prefer "mission of making a", but "mission to make a" is more frequent at Google Books.

The comma is important too.