Don't know about the 2nd (relativity and time dilation are well-established by experiment), but definitely agree with the first. The universe is dominated by plasma (electromagnetic) phenomena. The whole shape of our galaxy may simply be governed by electric currents over thousand-light-year scales.
Not as I've been reading it for the last ten or fifteen years, but that's a really long story.
There's no maybe about it. In real life 99.something percent of the mass of the universe is in plasma form and the one thing which actually can agglomerate matter on significant scales is the Z-pinch effect of cosmic Birkeland currents which actually are on the kinds of scales you mention, and that in fact is why we find strings of galaxies.