I'm one who often challenges the writings of Luke, who obviously had an inconsistency of the thieves on the cross with the other synoptic gospels. So in some ways I get sketchy with Acts. This is important as those simple verses in Luke created a complex issue that we can be "saved on our death bed" which kind of circumvents Jacob's ladder. The other gospels didn't speak of the thieves this way. So which gospel do you believe? Many say the Eastern Cross with the slanted bar reflects the story in the gospel of Luke, of course, it doesn't represent the other Gospels.
Could the Eastern Orthodox cross itself be erroneous? Matthew and Mark both said they insulted our Lord, yet Luke is pushed. The Eastern Orthodox cross could represent that we think a thief who insulted Jesus went to heaven.
If you want to go this route, then be prepared to take a machete to every Gospel except Matthew or Mark (depending on which you want your "base" to be). You seem to distrust the early Christians who preserved the faith for you immensely. Truth be told, I also struggle with this, but it's an "all or nothing" deal, and I can't accept any re-constructionist compromise.
Do we want to trust things that came from councils 325 years later and on held by a started by a world leader (Constantine)?
St. Constantine convoked the council, but did not rule over it. He also, therefore, added nothing to the apostolic faith, and any assertion otherwise finds no basis in any primary source.
What about Nazarite Christians?
Were "Nazarite Christians" (how do we distiguish between the Fathers' "Nazarenes", the Ebionites, etc) Gentiles? If they were not Gentiles, then the Council of Jerusalem does not refer to them.
Did Jesus teach worship on the Sabbath, or the 1st Day?
Both, but made the first day an especially Holy Day for worship:
Gospel of John:
So when it was evening on that day, the first day of the week
, and when the doors were shut where the disciples were, for fear of the Jews, Jesus came and stood in their midst and said to them, “Peace be with you.” And when He had said this, He showed them both His hands and His side. The disciples then rejoiced when they saw the Lord. So Jesus said to them again, “Peace be with you; as the Father has sent Me, I also send you.” And when He had said this, He breathed on them and said to them, “Receive the Holy Spirit. “If you forgive the sins of any, their sins have been forgiven them; if you retain the sins of any, they have been retained.”
But Thomas, one of the twelve, called Didymus, was not with them when Jesus came. So the other disciples were saying to him, “We have seen the Lord!” But he said to them, “Unless I see in His hands the imprint of the nails, and put my finger into the place of the nails, and put my hand into His side, I will not believe.”
After eight days His disciples were again inside, and Thomas with them. Jesus came, the doors having been shut, and stood in their midst and said, “Peace be with you.” Then He said to Thomas, “Reach here with your finger, and see My hands; and reach here your hand and put it into My side; and do not be unbelieving, but believing.” Thomas answered and said to Him, “My Lord and my God!” Jesus said to him, “Because you have seen Me, have you believed? Blessed are they who did not see, and yet believed.”
Gospel of Luke:
As they were talking about these things, Jesus himself stood among them, and said to them, “Peace to you!” But they were startled and frightened and thought they saw a spirit. And he said to them, “Why are you troubled, and why do doubts arise in your hearts? See my hands and my feet, that it is I myself. Touch me, and see. For a spirit does not have flesh and bones as you see that I have.” And when he had said this, he showed them his hands and his feet. And while they still disbelieved for joy and were marveling, he said to them, “Have you anything here to eat?” They gave him a piece of broiled fish, and he took it and ate before them.
Then he said to them, “These are my words that I spoke to you while I was still with you, that everything written about me in the Law of Moses and the Prophets and the Psalms must be fulfilled.” Then he opened their minds to understand the Scriptures, and said to them, “Thus it is written, that the Christ should suffer and on the third day rise from the dead, and that repentance and forgiveness of sins should be proclaimed in his name to all nations, beginning from Jerusalem. You are witnesses of these things. And behold, I am sending the promise of my Father upon you. But stay in the city until you are clothed with power from on high.”
Then he led them out as far as Bethany, and lifting up his hands he blessed them. While he blessed them, he parted from them and was carried up into heaven. And they worshiped him and returned to Jerusalem with great joy
, and were continually in the temple blessing God.