I didn't see what happened in the deleted thread, but judging between that and your several questions I guess it's best to take them one at a time.

How much of Julius Caesar's fame today is due to his consequentialism and/or skill, and how much is due to his writings about himself?

Caesar wrote far more than what we have now. We have the de Bello Gallico and the de Bello Civile. Sometimes other titles are used, but they almost all translate to "The Gallic War" and "The Civil War." The authorship of the later books is debated; it's probably Hirtius, one of Caesar's officers who wrote at least book VIII of the BG. It's almost certainly one of his officers. I think these each fit in a single Oxford Classical Text volume a piece, so it's not as though Caesar left a tremendous amount of writing for us.

In fact, he wrote far more than has survived. Off the top of my head I can name his poem Iter, his political tract Anti-Cato, and innumerable letters, and there are reports of many other things he wrote that don't survive, like the poetry he wrote while captive to the pirates. Cicero recognized Caesar as a literary genius in Caesar's own lifetime, on account of the two works I've already mentioned that still survive.

So it can't be said that our opinion of Caesar is unduly influenced by the sheer amount of writing he left, as we don't have nearly as much as we could have.

Is this detailed accounting of events unusual for a Roman leader?

Absolutely not. The Latin word for what Caesar wrote in the de Bello Gallico and Civile is commentarii: commentaries. We know lots of Romans wrote these things, and Cicero in a couple letters tells us what they're for. They are the "just the facts, Ma'am" accounting of the day-to-day business of whatever historical event they document, as far as we can tell. Caesar's are the only ones that survive. But we know Sulla wrote a commentary, and Cicero, among others. The purpose was to provide source material for a literary talent like Sallust, who would produce a decent literary history. We have letters from Cicero begging a historian to take up the topic of the Catilinarian Conspiracy (and to exaggerate Cicero's heroism, incidentally - literary flair is important). What is outstanding about Caesar's commentaries is, as Cicero tells us, they were already so good as literature that there was no use in getting a historian to write them up.

How much can we trust Caesar's writings?

As much as we can trust anything, I suppose. There is definitely a political line about the BC. People who don't like Caesar see his claims to defending the Roman constitution as opportunistic and hypocritical, while people who like Caesar see Caesar responding to a real constitutional crisis. A better criticism might be that when bad things happen to Caesar they are often the fault of incompetent subordinates. One example is early in the BG Caesar sent some men disguised as Gauls to take such-and-such a hill in secret. The next day he sends scouts to discover if his covert mission was successful. The scouts report back that the hill is held by Gauls. Caesar doesn't execute his planned follow-up, and later learns the "Gauls" on the hill were his advanced group. Stupid scouts, Am I Right? But Rosenstein has argued that sort of "passing the buck" was institutional in Rome in his "War and Failure" article, so that's not really unusual.

As for the one surviving quote from the deleted thread - why was Caesar popular? - I'm not sure that's true. There was a lot of myth-building that went on in the Imperial period, culminating in Shakespeare's speech by Marc Antony (which is a wonderful speech if you haven't read it). There are other people here who can better talk about Caesar's popularity.

Caesar's writings are important, but the Romans kept very extensive records for the period, and had many of their own contemporary historians. We don't have all of the primary sources anymore, but we have plenty of secondary ones. You don't have to trust Caesar's writings 100%, as the likelihood of significant embellishment is high, but he's not the only person who wrote about what he did, and the longer-lasting and further-reaching effects of his military campaigns. Even if he played up (or down) parts of battles, the end results are well-documented and agreed upon by his contemporaries.

Basically: Julius Caesar isn't famous because of his writings, his writings are famous because they're Julius Caesar's. Otherwise their greatest value would simply be the existence of such simple and direct prose for Latin instruction and Caesar would just be "That Roman general who wrote about a couple of his wars." The Gallic Wars wars were important, as the land mass added to Rome increased its size by almost half. But, it would still just have been a single war in a history full of wars. He subsequent civil war wasn't even the first, last, or largest civil war in Roman history, and if he'd quietly retired after that, it would be a chapter in a history book. Caesar's works were chosen for repeated preservation and translation because of who he was.

The time period before, during and immediately following his life were very consequential to the transition from Republic to Empire, and Caesar had a direct effect on so much of it. Even without his writings, we would still know about him. If anything, the writings on the campaign in Gaul and the subsequent civil war are only a portion of his life. Even if you include the later campaign narratives most likely written by one of his generals (or other closely-affiliated anonymous author), we're just talking about campaign logs. He was a political force in Rome both before and after his death, things we know of only through what other people wrote about him at the time, and in the subsequent two centuries.

The man's name became synonymous with preeminent political figures. The Roman leaders after him thought he was important enough that they used his name in order to carry some of that weight and authority, and the Holy Roman Empire after him kept it, lasting until the final Kaiser in Germany abdicated in 1918. Much of that is due to his nephew Octavian (Caesar Augustus), the man who is generally accepted as the first Roman emperor, but it is important to remember that the chain of events that made Augustus the emperor were largely influenced by the actions of Julius Caesar. Regardless of how much of that was Octavianist bias, the end result is that one man's name became synonymous with executive power, often sole executive power, for almost 2000 years.

He also made a lot of fundamental changes to the Roman government and society, including to the calendar which was used for close to 1500 years (of which the current calendar is just an improvement upon). Leap Years, for example, were an addition to the Julian Calendar.

Even if we just dismissed everything he wrote about as self-aggrandizing "I'm such a great general" propaganda. we still know about all the other events of his life. We're talking about the central political figure in the biggest transitional moment for one of the most consequential political entities in the history of Europe, perhaps the world. And he didn't get to that position simply by writing a bunch of puff pieces to make himself look good. Caesar isn't fooling audiences 2000 years later because he was a good publicist. He's famous because everybody in his own time took him seriously. Or, were forced to take him seriously, at times. If you wanted to make a short list of the most influential human beings in history, just in terms of how many subsequent events were shaped by their actions, Julius Caesar is going to end up on that list.

But, shorter and more directly, if the contemporary histories are to be believed, Julius Caesar was a really good general and an adept politician. He's not famous because we, or anybody else in recent centuries decided he was famous. He's famous because the Romans decided he was famous.