More punctuation questions

Hi there, I have some more punctuation questions if anyone is willing to help me out! I am trying to get my first novel self-published and just have the punctuation to go!

1. "Those things I said; I didn’t mean a word of it."

Is the semi-colon right here? Should it be a colon instead? Or em dash? I guess em dashes are more common in dialogue than semi-colons?

2. "And you, you spend your life trying to do the opposite of what I do."

From previous answers, I imagine the comma above is ok here?

3. "You’re just making excuses—rationalizing your behavior.”

Should I use an EM dash here? Or just a comma?

4. "I mean, was it really that awful?"
Should there be a comma here or nothing?
"I mean was it really that awful?"

Does I MEAN work like I THINK or is it more of a little filler expression so needs a comma?
What about if it was this sentence:
"I didn’t tell you about John because I want to be with him. I mean, not really."
Is the comma here ok?

5. I am this close to calling the whole second chance thing off.
I have put second chance in italics. Would that be right?

6. "“It’s been . . . it’s not been too bad."
Here, the character starts a sentence, then pauses, and says something slightly different. Is the above ok or does it have to be:
“It’s been . . . .It’s not been too bad."
Do you need to start a new sentence for something like this with a full stop after the ellipses?
How about if there were several changes of direction.
Is this ok:
“You...I...You’re...not disturbing."
Or does it have to be:
“You— I— You’re . . . not disturbing." using em dashes to show the sentence has been stopped?

7. After years of unnecessary injections of God knows what.

Does God knows what have to be in italics?

8. Maybe I’m not the only one who knows the truth about John; maybe other people do.
Is a semi-colon needed here? Or em dash? Full stop?

9. "John said it last time: most marriages don't survive such a loss."
Is the colon here ok in dialogue?

Thank you so much to anyone willing to give me some advice about any or all of these questions!

Monique