>>> If one believes in Jesus, they believe in the Trinity - Father (God), Son (Jesus), and the Holy Spirit.
No.
Jesus showed up and said he was going to save his followers from the destruction of Jerusalem. His warning did save those who heeded it. That was the "salvation" that the ignorant and faithless Jews needed. Jesus never mentioned that everyone needed salvation from original sin.
In addition to salvation from the destruction of Jerusalem, Jesus did miracles by asking his father with shamelessly. He promised whatever his students asked for shamelessly would be granted. He said that all the things he had done could be done by his students. He said that the disciplined would inherit the earth he never said "meek." Any Bible that says the meek will inherit is badly translated. Some Christians do seem to have worked miracles Saint Joseph of Cupertino comes to mind. Even Saint Paul struck a man blind temporarily, which was a neat trick.
Jesus did not teach that he was a person within a trinity. Jesus may well have considered himself to be the Messiah but that is assuming one particular interpretation of the gospels. You can go through the texts and argue that Jesus did not believe himself to be the Messiah. You can speculate about whether Jesus would have considered a Messiah to be a true embodiment of God you might as well speculate whether Jesus traveled to India, because the gospels do not give evidence for that either.
Jesus did not say that the kingdom of heaven was the afterlife. Jesus said the kingdom of heaven was within each of us. Jesus made some ambiguous comments about "all shall be salted with fire" but he did not expound any doctrine of a hell in the afterlife. Maybe he did believe in some kind of Hell, but there is no reason to think that he believed in the particular version of Hell that the Church invented later.
After Jesus had left for good, and after Saul called himself Paul and evangelized in a way that I doubt Jesus would have approved of, people collected their favorite books. The core of the early church chose some and rejected others. There is no reason to think Jesus would have endorsed their choices.
Jesus was awesome – and presumably still is awesome, wherever he is. Saint Paul seems ignorant and dishonest to me. The leadership of the early Church seems ignorant and dishonest to me. The doctrine of the Trinity seems false to me. The current major churches do not inspire my trust. (Maybe the Orthodox guys are better than the Catholics.)