Correct grammar, syntax, and spelling aren't optional. If your goal is to post stories online at sites like this (and there's nothing wrong with that), or if your goal is to self-publish an ebook, you can do whatever you want. However, if and when you ever work with a real publisher and professional editors, these are things that are simply not up for debate.
Ernest Bywater makes a good point with the image he provides demonstrating why the serial comma is indispensable. The serial comma has always been part of American syntax, but it is used in AP style. Because newspapers were once the most commonly read media in the US (other than the Bible, the punctuation of which is archaic), people sometimes assume American English doesn't use the serial comma. AP style omits many grammatical and syntactical conventions in exchange for ease of reading. A good reporter won't write a sentence that would be confused by its lack of a serial comma. Remember, newspapers are written for an audience with a fourth grader's reading skills.
Commas do not indicate a pause. They never have. Commas indicate the separation of clauses and sentence elements, especially when they diverge from standard sentence order (noun predicate indirect object direct object). We vary sentence structure when we write. If we didn't, our prose would be dull and limpid. That variation is enable by punctuation - commas in particular.
One thing that sets the pace of writing - tbh - is whether it's well written. If a reader has to stare at a sentence to puzzle out its meaning, you've failed. A writer never wants the reader to become aware of the fact that she or he is reading (in the technical sense). You want the reader focused on your story. Take a look at a seriously good writer's prose and note that the writer doesn't mess around with grammatical conventions. A good writer masters grammatical conventions so that she or he can accomplish, with proper usage, the things that some writers aim to accomplish by violating the fundamentals of grammar.
Sentence length, paragraph length, and the density of text on a page control the pace of writing. If there is more white space resulting from dialogue or frequent paragraph breaks, the reader feels as if the book is moving more quickly because the reading is moving more quickly. Short sentences accomplish the same thing. A long sentence takes our brains longer to parse. Even if it's a nanosecond of difference, our brains are capable of registering that. People think Hemingway is all about shot, rapid sentences, and he does use them frequently. But, if you read a lot of Hemingway and pay close attention, you'll see that he'll have long stretches of short sentences (that depict action) followed by stretches of long sentences where the character becomes less active and observes what's around him or her, which is usually a metaphor that Hemingway wants us to deconstruct.
Action moves quickly. Exposition moves slowly. Description moves slowly. Narrative summary moves slowly. Flashbacks somehow manage to move slower than just slowly.
This is not my most common complaint about authors, but, if this comment thread were representative of the authors with whom I worked, the largest complaint would be that they think basic line edits are optional. They're not. You're going to have an editor in your face who wants to cut two hundred pages out of your novel. That's what you save your fight for. If you get on an editor about a comma that belongs where a comma belongs, you'll be laughed out of the building as a ignorant and arrogant prima donna, and after you get back to your agent's office, you'll be lucky if the interns don't throw you out of a window for making trouble.
When I edit a piece freelance, it's the author's decision to accept the changes that I've made or to reverse them. But if I've been hired for what called "basic copyediting," the author is going to find it pretty darn difficult to replicate the bad grammar, the awful punctuation, and the misspelled words exactly as they were before submission. Don't pretend bad grammar is intentional. Let editors help you. That is what they volunteer their time for (or what you pay them for).
In his defense of the serial comma, bondsman notes that it should be handled consistently throughout a manuscript, and he's right. The problem with writers who are above proper grammar is that they may monkey with conventions in one chapter and, three chapters down the line, present a similar section of narrative with a different set of imaginary punctuation rules. The vast majority of writers who violate the rules of grammar and syntax - by far - do so inconsistently, and when the reader picks up on the inconsistency, the reader begins to doubt your competence and intent. The entire reason that languages have grammar is so that we have one primary method of expressing language. We don't have to remember a language we invented or modified, and a reader doesn't have to figure it out.
bondsman is also correct when he notes that there is an enormous difference between grammar, syntax, and punctuation and what we term "style" (which is not to be conflated with "voice"). A good editor will help you find your style and voice and make them more prominent and audible in your text. The editor's first step toward doing that is cleaning up your messy grammar.