1 Thessalonians is an undisputed letter of Paul. I don't know about 2 Thessalonians
Again, the most important Pauline epistles in the canon in terms of Christian theology, belief, practice, and ethics are all undisputed letters of Paul. You could get rid of all the contested letters and it wouldn't change the essence of Christian belief and practice at all.
Correct, Paul was not a rogue apostle just giving his own independent opinion, he was sanctioned by Peter and the Church in Jerusalem, aka the people who knew Jesus best.
There is no evidence anyone important ever called Paul's teachings heretical or rogue. All evidence points to the opposite: Paul's teachings were considered authoritative from early on. Any disputes Paul had with itinerant preachers was theological minutia.
The virgin birth narratives are not well attested and are basically irrelevant to the core Christian doctrines of grace and salvation. You could take the virgin birth narrative out and it wouldn't change anything about the essence of faith, grace, and salvation.
Jesus referred to himself as son of God on multiple occasions, and never denied the title when others gave it to him.
I have no idea why you are stressed out about the Trinity. While the canon does not specifically use that term, the triune nature of God is clear in the Gospel narratives and book of Acts.