Would you put the writings of Eusebius in the 4th century on the same level as the Scriptures of the 1st century? Was Eusebius ever wrong? What are his 1st century sources for his statements or is a lot of it hearsay and myth?
Yes! The Bible that you and I both cherish, was compiled by the Catholic Church. First off, is the Bible the "pillar of truth" in the Christian religion? No. According to the Bible Itself, the Church is the "pillar of truth" (1 Timothy 3:15), not the Bible.
Is the Bible the sole "teaching from God?" No. The Bible Itself states that their are "oral" teachings and traditions that are to be carried on to the present-day (2 Thessalonians 2:15; 1 Corinthians 11:2; 2 Timothy 2:2; Romans 10:17; 1 Peter 1:24-25). These teachings are what the Catholic Church considers "Sacred Apostolic Tradition." This type of "Tradition" never changes because it was passed down by the Apostles themselves. It is not the same as the man-made traditions condemned in Scripture. The man-made traditions condemned in Scripture were those of the Jewish Pharisees. In fact, as Christians, we are supposed to disassociate ourselves from persons who do not follow Apostolic Tradition (2 Thessalonians 3:6). If oral tradition is not to be followed, why did St. Paul state Christ said something that is not recorded in the Gospels (Acts 20:35)? St. Paul must have "heard" this saying, not read it from any Gospel or "Scripture," thereby, proving that some things Christ said were not recorded in the Gospels (John 21:25) and were passed on orally among His disciples instead, but were just as valid as anything written since St. Paul himself used one of these oral passages in one of his own epistles.
Did the early Christians have the Bible as we know it? No. The Bible as a whole was not compiled until the late 4th century and then it was compiled by a Catholic saint (St. Jerome) at the request of a Catholic pope (St. Damasus I). So how were the early Christians saved if they did not possess the entire written "Word of God" to follow His teachings? Well, naturally, they were the Body of Christ and were taught through "oral" teachings by the Church, not by writings.
Is the Bible to be taken literally - "word for word?" No. The Bible doesn't state anywhere that It should be taken literally. The Bible was written by different authors with different literary styles at different times in history and in different languages. Therefore, the writings should be interpreted with these circumstances in mind. The Bible is a religious book, not a scientific or a history "textbook."
So, yes, the historical record for Peter in Rome comes from extra canonical sources.