At the most basic level that can be substantiated, we know very little about Christian origins. What we know is that at some point a movement 'perceived' that God sent an emissary. Did they arrive at that through eisegesis of the OT and visions? Some comments in the extant writings of Paul would suggest that. There are scholars who argue that the 'soft' start of Christianity was a hundred years before the time the Gospel story indicates, as a branch of the Essenes. Regardless, it would seem that the death of the emissary was an original tenet of that movement, but to be honest, there were even early Christians who did not believe this emissary died either through docetic Christology or substitution. There were many rival factions that held many very different views at a very early point, that makes certainty regarding any 'original' form impossible. The writings of Paul, at best, represent a selection of what was written. Some 'letters' are collections of snippets have been heavily redacted and supplemented. Through critical analysis, what seems to be authentic, reveals a man who is convinced of his importance, having been chosen before birth to deliver a message received through visions. Contrary to the 2nd century Acts of the Apostles conversion story, he adamantly denies indebtedness to any human.
Paul is not the originator of Christianity; he encounters Christians of different types as he preaches his own unique form of the faith. However, his successes influence the broader Christian movement in profound ways a century later.
Someone deeply influenced was Marcion. What we know of Marcion comes unfortunately, through the writings of his opposers and those writings themselves are suspect of redaction/pseudonymity. Nevertheless, in those writings we read of a Marcion convinced that the dominant Proto-orthodoxy, of which he is part, has altered the texts of Paul and the Gospel of the Lord and claimed to have restored the original form. He resolves the contradictions of a vengeful God of the OT with his more refined take on Christianity by adopting the view that Yahweh was an imposter who had planned his own Messiah to rule the world through. He is charged by some of his opposers of having read the OT too literally. Marcion adopted the OT Yahweh demiurge concept from Gnostics, and claimed the true God was not this creator of the physical world , but rather the heavenly Father of Jesus, who was sent to enlighten and inspire humanity to better itself and thwart the efforts of Yahweh. No judgement day no hellfire, no miracles in the church. It was a kinder gentler form of Christianity that attracted many for 100 years. It seems impossible now to separate the OT from Christianity, but the reformer Marcion tried. What doomed his efforts was likely the celibacy requirement, lol.
As has been said many times here, the Canonical Gospels, especially the Synoptics, Mark, Matt and Luke, are anonymous recensions of the same anonymous work. They are not separate works, as can be seen by a parallel examination. G.Matt and G.Luke are rewrites of G.Mark, incorporating nearly the entirety of the shorter version verbatim, with many additions and redactions. The end products are different enough to pass as separate Gospels. The names attached to them is the result of a later effort to give them authoritative clout by the proto-orthodoxy with its doctrine of Apostolic succession (i.e. only works of direct companions of the Apostles can be authoritative) 'Luke', is a name mentioned in Paul's Philemon 24 as a "fellow worker". (The name reappears in the later Deutero-Pauline Colossians and 2 Timothy.) We know nothing else about Luke other than very late tradition and there is no reason to be convinced he was involved in the writing of G.Luke (or an early form of Acts which a later editor combined with it). There were many other Gospel versions in use that were not favored by the emerging orthodoxy. It was the golden age of pseudonymous Christian writing. The Gospel of Mark, itself anonymously produced, perhaps in Rome, has been convincingly argued to have been a narrative version of a stage production, in Homeric style, utilizing OT typology (and possibly Sayings Gospels) to 'flesh out' the emissary's experiences and make what may have been an already aging movement a new contemporary touch. It certainly influenced many Christians that followed. Paul, apart from some late glosses, seems to know of no such extensive tradition such as is described in the story of Mark. Neither does the author of Hebrews. Even Justin (150ish), (unlike Papias his predecessor) who favors written over oral tradition quotes from what he calls Memoires of the Apostles (a later gloss identifies them as Gospels) but doesn't use the names as assigned later nor does he refer to them as 'scripture' reserving that for the OT. If the extant copies of Irenaeus can be trusted, at some point between Justin and Irenaeus (180ish) the Gospels were given their names.