It depends on the nature of space, I guess. What happens to the parent universe while there's this enormous spatial expansion going on within it? I can imagine two possibilities:
1. The space of the parent is swept outward, pushed by the inflating space within it. That seems to require some kind of "substance" to space -- at least for this purpose -- which I don't understand, but I guess it's possible. The parent universe would end up surrounding the new universe. The most distant stars (if they existed in the parent) would appear far too old. This hasn't been observed.2. The inflating space simply "blows by" the existing parent universe and goes on expanding. The result is that the new universe ends up surrounding the parent. The parent region might be observable as a discrete portion of the visible universe, and (if it had stars) it would have older stars than we might otherwise expect -- but only if it were at the horizon of the visible universe, which it probably wouldn't be. If the parent universe were made of dark matter, it wouldn't be observed anyway.
Not necessarily. See "The Matter of the Bullet Cluster". According to these observers, gravitational lensing may make it possible for us to observe the effects of the mass of concentrations of dark matter on the light from distant galaxies.
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Right Whale: " Less than a century ago there were no galaxies. Everything was inside the Milky Way. Sometime between 1922 and 1960 the universe acquired galaxies..."
Not quite: from the northern hemisphere, there have always been two galaxies visible to the unaided eye: M31, the "Great Andromeda Galaxy" and our own galaxy -- visible from the inside-out as the "Milky Way". However, I agree that it wasn't until suitable telescopes were developed that we realized what they were -- and that there are lots of other galaxies.
BTW, & FWIW, in the photo at the above link, there are only a handful of nearby stars visible; all the rest of those white "spots" are galaxies...
In another comment, you bemoaned the lack of "C/E debaters" on this thread. Along those lines, I'll add that I can't comprehend how the "YEC" folks can "stick to their guns" after having seen photos like the one above -- or the Hubble Ultra Deep Field images... To me, those images make it impossible for me to accept Earth as the center of everything -- or the proposition that everything is only a few millenia old...