I'll answer your questions in parts, as I don't have enough time in the day to tend to them all at once.
The issue that arises immediately with this discussion is one of symmetry. The early three unified theories of gravity, quantum mechanics, and matter argued for conserved symmetries in regards to the fundamental identity of nature. This formalization of parity conservation was accepted by most in the Physics community and was coined the term "P-Conservation" In short, it was believed that the Universe was mirror image symmetric, that the enantiomer of this current Universe would behave exactly the same.
However, in the mid 20th century, it was discovered that we do not exist in such a strictly symmetric world. Examples of this asymmetry arose in a number of experiments. Such as the radioactive decays of certain atoms. In brief, the directionality of gamma-ray emission was not necessarily even in some atoms. Thus, the notion of a strictly symmetric Universe was abolished.
Indeed, this slight asymmetry in the world is required to explain the phenomena of the emerging Universe that does not completely annihilate do to perfect symmetry.
First, in order for any theory to explain the emergence of a Universe there needs to be CP symmetry violation. This was proposed theoretically shortly after the discovery of the slight antisymmetric nature of the Universe. This violation consists of two symmetry violations in quantum mechanics. The first, charge conjugation ( C ) operation of antiparticle transformation. The second, parity formation (P), the formation of the mirror opposite of a physical system. Indeed, once you have C violation, your system will naturally tend towards P violation. The details behind CP violation are best understand by way of Cabibo-Kobayashi-Maskawa matrix theory, which I won't expand upon to maintain brevity.
Second, there's a disequilibrium in the thermal state of the earliest chronology of the Universe. In short, the immense heat and density at the stage of the early Universe allows for an asymmetric Sphaleron transition. This results in asymmetric brayogensis, and thus a net result of either antibayrons of bayrons.