He may have a had a proto-gospel. He may have had some notes about the LXX (+/- other texts) he or someone else had made.
Moreover, with gospel = euangelion = good news, it may have just been an idea (+/- supplemented by certain concepts, written or not).
It would be a revelation2. did Jesus exist?
I doubt a tangible consistent Jewish Christianity did exist, at least not in Judea in the first century.3. was there a Jewish Christianity which predated the Christianity which emerges from the Church Fathers?
The narrative was set in the early first century AD/CE, of course.4. what year was the gospel narrative set?
Whether it - they- was set in stone before Codices Sinaiticus & Vaticanus were produced may be debateable.
Probably. It may have been Marcion's gospel (if several recent scholars' arguments are to be held).5. was there a gospel before canonical Mark?
Marcion? Someone before him? Around his time?7. who was the original gospel writer?
Good question. Supposedly writing from Gaul suggests he was an enigma. Or a visionary.8. who was Irenaeus?
Wasn't it ten Pauline epistles, his Euangelion +/- an Antithesis +/- a couple of other epistles ??9. what did Marcion's canon look like?
Isn't the first evidence of a congregation a 4th or 5th century bishop complaining his congregants turned to face the morning sun before entering his church?10. who were the first Christians?