(Added edit:) In the following post, I deal with OP's specific questions, which deal with some specific issues. If you're coming to this wanting some more general answers about related issues such as the development of the canon in the early church, or the growth of early christianity, here's a recent comment of mine on canon formation and here's an old but still good-ish post on the growth of Christianity.

Original answer:

To deal with your first question, the early church (in the first 6 centuries) considers “the Bible” or the Scriptures to be the Word of God in the sense that they are inspired, authoritative texts through which God has spoken.

As to how certain books ended up in the Canon, that is a slightly different issue (and I’ll get back to the connection between the two). The church took over the Hebrew canon, aka the Old Testament, wholesale, except for the fact that they almost universely used the Septuagint, the Greek translation of the Old Testament. So, Paul didn’t select any books. He treated the Old Testament as authoritative and inspired because he was a Jew.

Neither did the church conceive of itself as “choosing” books in the New Testament. They “had” books, and they recognised them or treated them as authoritative and inspired, usually by association with apostolic or near-apostolic authorship. The widespread acceptance of the New Testament books by Christian communities throughout the Mediterranean led to a formalisation of that collection, but it was a process over the first four centuries. It was not a “decision” by the church as an en bloc, collective institution.

And it certainly wasn’t a process that was still going on by the time of Justinian in the 5th century. The process of canon formation was essentially over by the late 4th century.

The concept that because human beings ‘chose’ the books in the Bible, then they could have chosen differently, and so the idea that the Bible is the Word of God is really a human construct, is anachronistic and not a fair representation of how early Christians thought about it. They didn’t conceive themselves as the abitrers of Scripture, deciding what was or was not God’s Word.

You are correct that ‘Shepherd of Hermas’ was recognised and treated as authoritative by some early writers such as Irenaeus, Clement of Alexandria, and Origen (at least early Origen). However it was not universally accepted, was seen as a later composition (now usually dated to the 2nd century unlike the canonical NT documents), and lacked apostolic connections. It continued to be read and used, but never gained the broad recognition required to be incorporated into the canon. Other books similarly ‘failed’ to make it into the canon, for similar reasons – late composition, lack of apostolic connection, perceived fraudulent authorship claims, incompatibility with early Christian doctrine, and lack of universal acceptance.

Does the Church review if a book should be included on a regular basis?

No. Well, no major, mainstream church does.

Do we know if later Emperors- Justinian and Constantine- altered parts of the Bible?

We’re pretty sure they didn’t, because the breadth, number, and dating of biblical manuscripts suggests that the texts we have, and our best textual critical constructions of earliest copies of those texts, predates those emperors and was not subject to change by them.

Could we argue that Christianity sprung out of the deficits of the Imperial Cult in Rome, which suggested that a man's worth was based on his military prowess? It was admirable to be cold and unemotional like Marcus Aurelius (further demonstrated in 'Hercules Furens' by Seneca).

One could argue that, but I don’t think with much merit. I suppose it depends on what exact claim one is pushing forward. If it’s an origin claim, not a slight chance. There’s no doubt that Christianity emerges in an early Jewish milieu, centered in Galilee and Jerusalem, and makes the ‘jump’ to eastern Mediterranean Hellenistic culture and cities relatively early (the late 40s/early 50s CE).

If it’s an argument for why Christianity was successful, it becomes a lot more complicated. Not least because the Imperial cult flourished in the Greek-speaking east to a much greater extent than it did in Rome itself. I’d want to hear more of an argument for why, what deficits Christianity addressed that were particular to the Imperial Cult, and why the Imperial Cult, as opposed to other religious phenomena in the Greco-Roman milieu, is the key issue.

Did the Germanicus Wars and various famines not show the need for charity and compassion? Did this demonstrate to the population that a cohesive society needed such qualities, thus attracting many followers?

I wouldn’t think so. There’s no consistent evidence or research that I’m aware of that suggests these phenomena led to widespread cultural shifts or value-changes that were themselves influencers towards growing Christianisation.

If I may add another question - why was the Didache not included in the canon? I am lead to believe that it is linked to apostolic tradition, and is not entirely dissimilar to what was circulated by the church after the Council of Jerusalem (included in Acts).

If I may add a question:

6. It has been mentioned here and there, that ancient texts where found that showed a different view on women in society during that time - and there is the claim that these texts where left out because the content was not in unison with a male dominated European society, thus the people who selected which texts to include in the Bible feared it would have negative impact if such things would be taught. The conclusion being more or less, that this is the reason why women had been inferior for centuries.

Is any of this true and if so what is known about these texts? Is there a way to study them and/or are there copies online? Is there a discussion about adding these texts to the current Bible in order to have a more complete version? Or are these just of historic value?