The New Testament relies heavily on Old Testament writings, events, metaphors, the works. The New Testament often assumes familiarity with the Old Testament. The New Testament often "sees" itself in continuity with and fulfilling the Old Testament. For example, Jesus died on the cross as a sacrifice for sin in a similar fashion to the way the lambs were sacrificed for sins under the priestly system that went back to Moses in the days when the Ten Commandments were given. So John the Baptist looks at Jesus and says, "Behold the Lamb of God who takes away the sin of the world" (John 1:29).
I'm not sure what you mean by "pre-biblical" writings since parts of the Old Testament are among the most ancient writings known to be in existence, but there are middle eastern writings, for example, that were apparently contemporaneous to parts of the Old Testament which one is certainly free to read for oneself, though some of these are less readily available, expensive, and not necessarily at all challenging to the Christian religion, e.g. the Epic of Gilgamesh, the Code of Hammurabi, the Amarna Letters, various accounts of various Egyptian kings, business letters from Sumer, or later for example the Apocrypha, a collection of Jewish writings chronologically falling between the two testaments, of which perhaps 1 Maccabees is the most important, recording the Maccabean revolt against Antiochus Epiphanes IV and the beginning of the Hanukkah festivities.
But as a newbie, best major on the majors: the whole Bible, both Old and New Testaments. Granted, Jesus is the apex and culmination of God's revelation to man--the top of the mountain, so to speak. That is the Christian belief and mine as well. So by all means familiarize yourself with the Gospels (Matthew, Mark, Luke, John) and apostolic writings (e.g., the epistles like Romans and 1 Corinthians).
One can of course also stray doctrinally reading the New Testament or both testaments. The Holy Spirit must also be present to prevent that. And certainly mature chaplains can be used of the Spirit to correct early doctrinal waywardness. This is in part because the church generally is a repository of the Jesus-tradition from the Scriptures and originally from the eye-witness disciples and from Jesus Himself.
Churches have been wrestling with the Scriptures and doctrinal issues for many hundreds of years (ever heard of the Council of Nicea (Nicaea) and the Chalcedon Definition?--Google them), and a trained chaplain would hopefully have some awareness of that history and lean in part on the conclusions of that tradition.
But as you can tell from schisms and denominational differences (e.g., Eastern Orthodox, Roman Catholic, Protestant), those who call themselves Christian have had disagreements, some of them major doctrinal ones. So it depends on which chaplain you rely on as to how your doctrine might be influenced.
I would suggest using your own reading of the Scriptures (the Bible) as a major guide and chaplains or ministers or mature lay Christians as secondary ones. I would not recommend going it alone doctrinally, but in the last two millenia, probably some group or other has already argued for whatever new interpretation you might possibly come up with.
I would also recommend always clinging onto the most fundamental, basic, or certain doctrines such as the identity of Jesus and what He accomplished on the cross. And I'd recommend working at your thought and study of the Scriptures and of the doctrines of the church over time. I've been working at it as an adult for over thirty years to date.
Does that help?
