Roman Jewish Historian Josephus.

Repeating stories he heard decades later. Hearsay by people who had an incentive to lie. Josephus also said things like this:

Now Adam, who was the first man, and made out of the earth, (for our discourse must now be about him,) after Abel was slain, and Cain fled away, on account of his murder, was solicitous for posterity, and had a vehement desire of children, he being two hundred and thirty years old; after which time he lived other seven hundred, and then died. He had indeed many other children, 1 but Seth in particular. As for the rest, it would be tedious to name them; I will therefore only endeavor to give an account of those that proceeded from Seth. Now this Seth, when he was brought up, and came to those years in which he could discern what was good, became a virtuous man; and as he was himself of an excellent character, so did he leave children behind him who imitated his virtues.

It's interesting to me that you consider him a valid source for one thing you can't prove but reject pretty much everything else the man said especially since you can't really disprove the Adam and Eve story.

Enough so that secular historians consider the person known as Jesus of Nazareth to be a historically real person

Interesting because your boy Josphius was in the area and wasn't aware Nazareth even existed. In any case truth doesn't depend on how many people assert something.

His ministry wasn’t even that uncommon at the time. There were many apocalyptic preachers around that time and other magicians/miracle workers, like Simon the Magician.

And?

We know this because a group of followers doesn’t just form and grow without someone they are following. The entire teachings of everyone within his group revolves around Jesus, and if he didn’t exist then Christianity never began. People need a leader to form a group, they don’t just all be together and say hey, let’s make up a dude and then follow what we made up. They believed enough to die for their group, and they believed enough to dedicate themselves to growing it. That doesn’t just happen if you made it on a whim or made up a key point of your story which could be validated. Additionally just because books were written multiple decades later doesn’t mean that they were completely made up. People can live multiple decades, and stories of experiences and knowledge of people can survive this long easily too. We also don’t know what they knew at the time because lots of information about Jesus that would have survived had been altered much much later by kings who wished to use Christianity for control, we of course know he didn’t completely make up Jesus as there are books referencing him from before this happened, however it does mean our information now is more limited than theirs, so we can’t assume they made this up based upon the same information we have now. It is both logical and just true that they would have had access to more valid information than we do today. They where also often scholars who’s job it was to write about true people and to prove together missing info and validate this sort of thing is even real. With all the information that was available at the time they still believed he existed. We can’t say just because such evidence was lost doesn’t mean that they all came to an invalid conclusion or all made it up. It’s just illogical. As for actual biblical events that had few witnesses, it’s fine to believe that that was made up, or information was lost so it was believed that something happened when in reality there is an entirely different reality that we just don’t have what we would need to piece together today. As we are assuming many stories are being made up or are incorrectly accounted throughout it, it’s not fair to say any events in his life happened based on the book alone, so this a mute point.

TLDR Jesus was real because he formed a group that still exists and followed his teachings from the beginning. Groups don’t just form and follow a fake persons teachings and still believe it and constantly lie about his existence. Scholars closer to his life who had more information than we do now believed he existed, and we can’t invalidate multiple scholars with more information than us just because we don’t have that information anymore.

I am always curious about how the Jesus was real crowd explains all these things Jesus supposedly taught that no one seems to know about until about fifty years later. And why these things he taught just happen to be from a subset of the Greek OT that was popular at the time. Strange how an Aramaic speaking rabbi, in an area with a 1% literacy rate, would only quote from a book written in Greek. And no one is aware of these parables and sayings.

According to Paul these are all the things that Jesus taught:

1. Don't get divorced and if you do the woman is never to marry someone else

2. Pay your preacher

The second one is debatable as well.