Current Cosmology

I watched part of a TV documentary about the latest findings in cosmology and cosmography and found some of these findings surprising - although they will have to inform any future cosmological sf of the kind written by Olaf Stapledon, Poul Anderson or James Blish.

My Understanding Of What Was Said
(i) Space is flat, therefore the universe is infinite.

(ii) The observable universe is a large but finite sphere within the infinite universe.

(iii) The observable universe extends for as many light years as there have been years since the Big Bang. (Does this mean that the observable universe expands at the rate of one light year per year?)

(iv) The observable universe is mapped by measuring the apparent luminosity of supernovae in remote galaxies.

(v) The entire universe expands not because the galaxies move through space but because the space between galaxies stretches.

(vi) Most (73%?) cosmic mass is invisible dark matter. (See Addendum below.)

(vii) The presence of dark matter is detectable both because of its gravitational effects and because it distorts light waves.

(viii) Gravity counteracts cosmic expansion and might have caused a cosmic collapse, as in Anderson's Tau Zero.

(ix) However, a more powerful force called "dark energy" counteracts gravity and causes cosmic expansion to accelerate. (Does this mean that other galaxies will eventually leave the observable universe?)

(x) There might be an infinity of infinite universes.

(xi) A collision between universes would have effects detectable within our universe.

(xii) These hypothetical universes are simply other universes, not the branches from our universe hypothesized in quantum mechanics.

Addendum: I have just googled dark matter and dark energy and seen that it is the latter, not the former, that is believed to comprise most of the universe.