In short: you're correct.
Long-form:
The use of "so" in
You're so not cool.
is extremely idiomatic, and informal. It's used to emphasize the degree to which "you" are "not cool". The result is a superlative statement, in a way, declaring the level of "not-cool-ness" to be extreme, and beyond measure. Verbally, the word "so" would be strongly stressed.
Compare:
You're not cool.
You're so not-cool [that I'm at a loss for words to express myself further].
This construct would be well placed in the film "Mean Girls", delivered as an insult with a dismissive and exasperated affect.
Conversely, placing "so" after "not" is much more thoughtful, (though still critical.) In this case the sentence suggests that the listener has an overly-inflated ego, or perhaps that the speaker formerly thought that the listener was once a "cooler" person than they are now perceived to be. The "not" is used as a polarity switch, and "so" is used as a modifier of "cool".
Compare:
You're so cool.
You're not so cool [as you think you are/as I thought you were].
This phrasing would likely show up in a light comedy scene, as a form of criticism, but lacking malice. It could be said between friends, and be at least forgivable, or maybe delivered and taken entirely as a joke, or "ribbing".
One may notice here that, as is common in English, both examples are used as shorthand to express a longer idea, which I spelled out in [square brackets], making them both "jargon", and incomplete in themselves.
Citing my source: I'm a native speaker of American English, raised in California, with some college, several years of customer service communication, and an author for a parent. Practical linguistics is a hobby.
Ago measures a length of time into the past from now (the present).
At ten o'clock, an hour ago was nine o'clock.
A year ago is (approximately) 365 days previously.
In quoted speech ago is used to refer to a length of time prior to the speech: In 2010 he said, "I gave up smoking three years ago."
Before marks a period prior to a particular point/day/year in history or an event/period.
Before means prior to/earlier than a time/date or an event.
Unlike ago, before does not usually relate to now
Before can refer to the past (*before he died) or to the future (before she arrives). It is always tied to a particular time or event.
Best Answer
For the pattern in your example
The usually pattern is
such being used as a superlative expressing a "high degree" or being "exemplary" of an adjective.
Being "such a hustler" is having more "hustle" than just being "a hustler".