Jesus Christ as god on Earth and the trinity. Are these things that have been normal part of Christianity since the beginning?
Yes.
No. There were many beliefs in the first 300-400 years of Christianity regarding Jesus and the so-called 'trinity'. Many didn't believe this at all. Many in the church thought Jesus was just a human that spoke well.
Roman emporer Constantine, in 325 AD (the Council of Nicea), gathered together Bishops from around the Roman empire because there were so many varying beliefs on whether Jesus was the 'son of god' or just a man and many other questions regarding deity re Jesus.
These Bishops then VOTED on what would be Christian dogma, i.e. that Jesus would be thought of as deity rather than a man. It was rule of the majority. It had nothing to do with 'godly inspiration'. The views of the minority were crushed and expelled.
It would be similar to Bishops from Protestants, Catholics, Baptists, Prebyterians, Calvinists and every other Christian sect having a meeting and voting on which single sect would be the winner and be taught as the official dogma of the church. The losers views discarded as rubbish. It was worse then because different sects would actually war on each other for their differing beliefs. More like what we see in the split in Islam in the middle east today.
Made absolute law by a Roman emporer, voted on by human beings. It wasn't divinely inspired. It was human politics, and the losers beliefs were crushed.
Add to this that there were many books that were left out of the bible. If they are inspired by god, what would you call it when humans reject god's word and decide what is and isn't contained in the bible?
This is what you believe is rock solid and has always been. It hasn't. Christianity is a mess of political forcing and compromise all along the way, as are all religions.
Many atheists know more about your religion than you ever will.
And I'm not a pagan, that seems to be your pet word for 'other'. I'm an agnostic.