Is neutronium a thing? Cite your source

In order.

No.

Possibly over time they will achieve critical mass to collapse to a singularity but unlikely. More likely is that their mass will be eaten by another black hole.

Yes, each star formed from a hydrogen cloud on their own as there were no galaxies. It is the death and birth of the first stars over and over that gave rise to the localised clouds of gas and matter that became galaxies as their density increased.

No one knows what Dark Matter is and we only know it is there because there is a gap. If Dark Energy interacts with matter then we have so far been unable to detect it whether on a macro, micro, atomic or quantum level.

No,God Made It!