Jewish scholars in Alexandria translated the Hebrew Bible into Greek, a version known as the Septuagint.
Using the Bible itself to prove anything about the Bible is an example of what is known as circular reasoning. It relies on the Bible to be divinely inspired and inerrant in order to be useful evidence that it is divinely inspired and inerrant. Therefore, any evidence as to whether the Bible is divinely inspired must come from outside the Bible and be independent of the Bible.
There is no extra-biblical evidence that the Bible is divinely inspired. In fact, the Bible's many errors and inconsistencies militate against divinely inspiration. Speaking of the two gospel genealogies of Jesus, Raymond E. Brown (An Introduction to the New Testament) says, "Inspiration does not guarantee historicity or reconcilability; otherwise God should have inspired the two evangelists to give us the same record."
The six "commandments" mentioned by Jesus in Luke 18:20 are a subset of the famous 10 mentioned in Exodus and Deuteronomy. The corresponding passage in Matthew lists 5 of the famous 10, plus one other that Jesus, at one other time, listed as being one of the first and greatest commandments. The key to understanding this section, though, is to realize that one cannot take a verse or two out of context and expect it to mean much. Many cults and individual flakes have done this over the centuries. It doesn't work. Instead, read the whole section, and take it in light of the entire Bible. By the way, the context of the Bible reveals that merely following commandments doesn't get one into Heaven. James 2:10 tells us that a person who has broken even one of God's laws is as guilty as someone who has broken every single law. Romans 3:23 tells us that nobody (except Christ, though that's revealed in context, not in that particular verse) is without sin. Instead the law was given as a "tutor," to bring us to Christ in faith (Galatians 3:24). Matthew 19:17-19 . . . if thou wilt enter into life, keep the commandments. He saith unto him, Which? Jesus said, Thou shalt do no murder, Thou shalt not commit adultery, Thou shalt not steal, Thou shalt not bear false witness, Honour thy father and thy mother: and, THOU SHALT LOVE THY NEIGHBORS AS THYSELF. "Thou shalt love thy neighbor as thyself" is not on Mark's or Luke's list of Jesus' Commandments . Mark 10:19 Thou knowest the commandments, Do not commit adultery, Do not kill, Do not steal, Do not bear false witness, DEFRAUD NOT, Honour thy father and mother. "Defraud not" is not on Matthew's and Luke's list of jesus' commandments. Luke 18:20 Thou knowest the commandments, Do not commit adultery, Do not kill, Do not steal, Do not bear false witness, Honour thy father and thy mother. Luke only listed 5 commandments. There was no 6th.
The terms are pretty much synonymous. They both refer to a religious deviate. Heresy was coined by the early Roman Catholic church to refer to those deviated from the Catholic Church. The term Apostasy is used by the Bible to denote one who strays from the pattern of truth found in the Bible. Often the term "apostasy" will refer to one who has declared a belief or affirmed an attachment to a set of beliefs, but later attempts to lead other adherents to stray from those beliefs; "heresy" is often used to refer to a similar situation led by a non-adherent.
Anybody can declare a new Doctrine; but the question really is, will anybody adhere to it? The authority to declare doctrine varies depending on the Christian denomination, and I presume that it varies through time. Anybody can declare doctrine, but whether that doctrine survives depends on how many adhere to it. And I suspect the number of adherents depends on how useful the doctrine is to various individuals. In a free country, there is no official declarer of religious doctrine. In the Roman Catholic faith, the pope declares doctrine. In the Orthodox Christian faith, only a Church Council or Synod declares doctrine. In Protestant groups, anyone can declare their own doctrine.