do you also think that much of what many early Christians' believed has possibly somewhat been manipulated limited or distorted through the lens of 2000 years of history ?
In some cases yes, and still so today. There are some 'sensational' views of early Christian history around today, books even making it to the best-seller lists.
And there is more sober scholarship, but those books tend not to gather media attention, and not having anything particularly sensational to say, tend to pass without comment.
What documents would we study about early Christians' and their beliefs ?
Depends what era you're talking about.
as far as I have found, there are not that many documents existing outside of the documentation that is found in the Roman Catholic Church that summarizes what the Roman Church Leaders had to say about Non Catholic " so called " heretical or erratic faiths,
We need to be careful about anachronisms here. If there were representatives of the Greek Orthodox or other Patriarchates here, they'd come down quite hard on you for this. The 'Roman Catholic Church' was not the entity then as it is now.
Are the only documentation available for us to study centered specifically around the the trinity - the human and divine disagreements of God and argumentations between the Catholic Church and those who they castigate as hereticks
The Arian Controversy
Most of these heresies rose within the Eastern Roman Empire, and were Greek-based rather than Latin-based. The then Pope regarded Arianism as a local problem in Alexandria – where it arose – and saw no need to get the whole church embroiled, as it were. It's only when political players got involved that it became such an issue.
it seems everyone else were not able to preserve their faith in writing, are the only surviving documentation that exists today are what the Roman Catholic Church has preserved about those who they deemed as heretical. ?
The problem here is that writing and recording was a long, expensive and laborious process. And the materials were fragile so had to be periodically recopied to be preserved ... so yes, obviously no-one saw the need to preserve the works of heretics for posterity.
In the same way, even the works of the orthodox were lost ...
As a context, De Rerun Natura (The Nature of Things)
, a work by the Epicurean poet-philosopher Lucretius (c99-55BC) was lost until a single manuscript was discovered in 1417, in a library in a Benedictine monastery at Fulda.
The oldest complete text of Homer's Illiad
dates to the 10th century, later gifted by Greek Cardinal Basileus Bessarion along with his library of Greek manuscripts to the Republic of Venice in the 15th century.
Seneca's writings were widely admired, and again versions turn up in monastic libraries, but again, one of the oldest extant texts was lost in the 12/13th century (from a civil collection)
It's the same for almost every ancient literary giant – there are references and citations, but so often the actual text itself is lost.
So it's not so much that so little has survived, as anything survived at all, in a continent ravaged by wars left right and centre, especially after the fall of the Roman Empire, in many places the monasteries kept the flame of scholarship alive, and so transmit such texts to us.