I think you're confusing time with space. There is clearly a "time" edge to the universe, the big bang itself. But there is no evidence for a space edge of the universe. Yes, we don't have much evidence for what exists time-beyond the prototype galaxies. But we have lots of evidence for what is space-beyond the prototype galaxies. Namely, it will look like every other region of space that we can see. Relativity and the isotropy of space demand it. (i.e. if an alien grew up in one of those prototype galaxies that is ~13+ billion light years from here, and space beyond it was different somehow, then space wouldn't be isotropic for that alien. And that alien would have the same question about what is beyond our galaxy - we WERE the 13+ billion light year distant prototype galaxy for lots of the observers in the universe.)
In any case, knowing what happened in the early universe is completely irrelevant for what is causing the dark matter effect in galaxies today (other than, of course, whatever causes the dark matter effect was probably created in the early universe). Flying spaghetti monsters could have roamed the early universe, it doesn't matter. Only things that survived until today can be causing it.
True. That experiment has been done, see http://en.wikipedia.org/wiki/Massive_compact_halo_object
There is much wrong with everything else you say. First, black holes can't be only at the edge of the universe. There is no edge - the universe is isotropic, as far as we know. Unless you suggest that the black holes were in the early universe but have somehow vanished over time. But in any case, that is totally irrelevant. We see dark matter effects IN galaxies NEAR us that we can see ALL of. If all the black holes are at the edge of the universe, they aren't affecting the dynamics of the galaxies we can see, and thus can't be cause of the dark matter effect.
No it isn't. The job of the lawyer is to advocate for his client. Suggesting to the clients dumb ideas which won't work and will only end up costing them legal fees is not advocating.
Mirrors should reflect a little before throwing back images. -- Jean Cocteau