I think you will find that the NWT NT is based on the Greek text of Westcott and Hort, as against, for example, the KJV NT which is based on the Textus Receptus, or the NIV which is based on an eclectic mix of sources.
I cannot comment on their OT, whether it is based on the OG (=LXX) or on the MT. There are several differences between the Hebrew and Greek, as well as with the versions in the DSS. Most of the NT citations from the Hebrew Scriptures are from the several vesrions of the LXX (even words attributed to Jesus) rather than from the MT.
I think you will find that Theodotian (381 CE) was more responsible for enforcing the Trinity and for determining Christian orthodoxy. The final list of which writings would be accepted the NT was drawn up by the Trinitarian Athanasius. Unfortunately he made mistakes, because Paul did not author several of the writings attributed to him, such as Ephesians, Colossians, 2 Thessalonians, 1 and 2 Timothy, Titus and Hebrews, as well as some small parts of Romans, 1 & 2 Corinthians.
For example, whereas Paul says there is neither male nor female and all are one in God's sight, that it would be better that they not marry or have children, and he used women to teach, a mysoginist writing 50 years after Paul died said that women were to be subject to their husbands, and they would be better to be silent and pregnant, and that the leaders had to be married.
The NT writings that were canonised represent the views of the Paul sector that became the dominant force, under the protection of the Roman emperors.
If you would like to read some of the history around the formation of the scriptures, which took centuries of deep division, try these for example:
"Who Wrote the New Testament?: The Making of the Christian Myth", Mack
"AD 381: Heretics, Pagans and the Christian State", Freeman
"A New History of Early Christianity", Freeman
"Jesus Wars", Jenkins
The 4th and 5th centuries saw murder and mayhem between the Christian factions that leave the Spanish Inquisition in the kindergarten league.
It is possible to read some of the writings that were not included in the NT by Athanasius:
"Lost Scriptures", Ehrman
"The New Testament and Other Early Christian Writings: A Reader", Ehrman