A very good set of questions! I researched this stuff ages ago, when we went to church and then SWMBO volunteered me to do Sunday School.
Sunday School turned out to be much less boring than the sermons and I thought I might actually know what I was supposed to be "teaching them about Jesus". So:
1, Almost certainly something like Joshua. As pointed out above, "Jesus" is actually a Mexican name and will derive originally from a transliteration into the romano-greek style on masculine nomenclature.
2. Aramaic - the language John Mark scribbled the first account of his life in, with the added bonus of using a Greek vocabulary wrenched into his Aramaic grammatical rules. Christianity is a Greek phenomenon.
3. All half serious biblical scholars believe in the notion of "Markan Primacy". That is that John Mark of Jerusalem (or some other kid, no real need to enquire) scribbled out the sayings of Simon (whom the Lord called Peter) some time shortly after the time of the deaths of both Peter and Saul of Tarsus. The said Mark was a disciple first of Saul (Paul) and then of Peter. Matthew is a copy of Mark which incorporated both some mythological stories of the deeds not only of Jesus but his alter ego- the risen Christ, or Jewish Messiah, and some weird nonsense from the Old Testament, which was supposed to convince a sceptical Jewish audience that Jesus was the promised Messiah. Matthew the gospel writer and Matthew (or Levi, son of Alpheus) cannot be and were not the same person. Absolutely no even half serious biblical scholar would believe anything else.
4. John emanates from Ephesus, then the most important port in the eastern Mediterranean, at the very earliest, in the second century AD. Only 9% of its content can be found in Mark (feeding of 5,000, passion narrative...) or the other so-called synoptic gospels (Matt and Luke). In short, John is a work of an oral tradition, or, better, mythology about a "risen Christ", a figment of the imagination of the epileptic mind of Saul of Tarsus.
