Most ancient Greek sources say Chaos is the first primeval god. Chaos was the empty void from which all things sprang. Although, some Greek sources say Chronos, the god of time, was the first.
Primeval 'matter' without any characteristics that everything evolved of
They were born of older primeval gods and goddesses of creation.
Minotaurs do not exist, it was a creature from Greek mythology
In Greek Mythology, yes.
No, it is a creature in Greek mythology
No.
Janus did not exist in ancient greek mythology.
Greek Mythology pre-dates Noah and the tales of the Bible; so, yes, it did, so too did Egyptian Mythology.
The ancient primeval gods (first-born elemental gods) or "Protogenoi" of Greek mythology were the basic components of the universe which were emerged at creation; of which Nyx was counted among.
Chaos was the first primeval goddess to appear at the creation of the universe.
Yes, they are a part of Greek beliefs, and are in Greek stories, but that does not mean they do not exist.
No. The devil does not exist in Greek Mythology.