Comma after "You know what" phrase

As a Russian-speaker, these two usages remind me of the Russian phrases "Знаешь, а..." and "Знаешь что?". However, I feel like their usage varies with the language.

In English, you can only use "you know what?" as a question, typically to show that you've come to some conclusion, made a decision or simply agree with someone (e.g. "You know what? That's not a bad idea!" in the sense that "On second thought, I like that idea too"). However, it can also show that you're fed up ("You know what? I can't take it anymore, I'm out).

You can use "you know" in an affirmative sentence to convey agreement ("You know, that's not a bad idea!"), to seek understanding or sympathy ("I just understood that I couldn't stay there anymore, you know?"), or to make a point ("You know, I don't have time for this").

But, in both languages, there's an interrogative version, and an affirmative version.