The primary set of texts held to be true are what is generally agreed upon as the earliest texts.
These are the short, the long,the middle length, the connected and the numerical discourses of the Buddha as well as discourses in the Udana and Itivuttaka.
These are generally held to be the written version of what was historically recited in concert for hundreds of years.
Loosely one can assume these were written down in the 1st century.
Around that time the various schools also wrote down whatever else they figured to be worthy of being written down. This is the secondary class of texts.
As we talk about this latter set of texts, it is important to keep in mind it will include the works of many schools with views antagonistic & contradictory to eachother.
Some of the texts in this category are supposedly analytical of primary texts whereas other texts aim to more or less substitute the primary discourses altogether.
This period of secondary produce lasts for 100-300 years and a lot is produced during this time. These are primarily the works of philosophers and disciples.
Basically 1-3rd century is when the various schools consolidated their doctrines by comitting it to writing.
After this period and up to present day the various surviving traditions keep producing commentarial and sub-commentarial works of disciples, poets and philosophers.
It is also worth mentioning that commentating is essentially a free-for-all activity and whoever had access to the texts and writing could write commentary if they wanted to do so.
There are many attempts at a popularization & simplification of the teacher's message made even during the last 50 years.
As you can perhaps imagine, getting through even just that which was committed to writing before the 3rd century might take tens if not hundreds of thousands of hours.
If one was to thoroughly study the Buddhist texts in a reverse chronological order, starting with the lastest public discourse, i think it would be next to impossible to get through the sheer volume of text and more so doing it without becoming utterly confused.
That being said one can attempt to cross reference the public discourse with the earliest texts and this is imo the most effective way to familiarize oneself with both. Whether one wants to participate in & study the public discourse is a moot point but i think most people will expose themselves to the public discourse and pick the brain of their peers.
There are some texts produced in the last 50 years which are essentially excerpts from the earliest texts and sometimes with comments, these are supposedly meant to be introductory to those earliest texts but as it seems to me, the authors sometimes have a hard time not including their speculative interpretation or making doctrinal insinuations.
Another thing is that when cross referencing the public discourse and studying the controversies one will inevitably be faced with the issues associated with translations and this translation activity is also a free for all. You can totally expect having to learn some pali and maybe some chinese to find the correct translations and to make your own if you want.
In general this is the teacher's instruction on the matter of studying & training:
When beings are degenerating and the true Dhamma is disappearing, there are more training rules and yet fewer monks established in final gnosis. There is no disappearance of the true Dhamma as long as a counterfeit of the true Dhamma has not arisen in the world, but there is the disappearance of the true Dhamma when a counterfeit of the true Dhamma has arisen in the world. Just as there is no disappearance of gold as long as a counterfeit of gold has not arisen in the world, but there is the disappearance of gold when a counterfeit of gold has arisen in the world, in the same way there is no disappearance of the true Dhamma as long as a counterfeit of the true Dhamma has not arisen in the world, but there is the disappearance of the true Dhamma when a counterfeit of the true Dhamma has arisen in the world.
"It's not the earth property that makes the true Dhamma disappear. It's not the water property... the fire property... the wind property that makes the true Dhamma disappear. It's worthless people who arise right here [within the Sangha] who make the true Dhamma disappear. The true Dhamma doesn't disappear the way a boat sinks all at once.
in the course of the future there will be monks who won't listen when discourses that are words of the Tathagata — deep, deep in their meaning, transcendent, connected with emptiness — are being recited. They won't lend ear, won't set their hearts on knowing them, won't regard these teachings as worth grasping or mastering. But they will listen when discourses that are literary works — the works of poets, elegant in sound, elegant in rhetoric, the work of outsiders, words of disciples — are recited. They will lend ear and set their hearts on knowing them. They will regard these teachings as worth grasping & mastering.
"In this way the disappearance of the discourses that are words of the Tathagata — deep, deep in their meaning, transcendent, connected with emptiness — will come about.
"Thus you should train yourselves: 'We will listen when discourses that are words of the Tathagata — deep, deep in their meaning, transcendent, connected with emptiness — are being recited. We will lend ear, will set our hearts on knowing them, will regard these teachings as worth grasping & mastering.' That's how you should train yourselves."
"... there is the case where a monk studies the Dhamma: dialogues, narratives of mixed prose and verse, explanations, verses, spontaneous exclamations, quotations, birth stories, amazing events, question & answer sessions. He doesn't spend the day in Dhamma-study. He doesn't neglect seclusion. He commits himself to internal tranquillity of awareness. This is called a monk who dwells in the Dhamma.