It would develop into "regions" of space that are entirely matter and others that are entirely antimatter. The boundaries between them would glow as stray particles drift between the regions and are annihilated by contact with the opposing particles.

The fact that we don't see these glowing boundaries in space is evidence that there are not antimatter regions and that the visible universe is almost entirely composed of matter.

It would depend on how it's distributed. If it's very homogeneous, totally anihilated. If there are galaxies of matter and galaxies of antimatter, more or less like us with a bit more background radiation.

Very, very bright.

Annihilated.