Punctuation

Q. Is it “Hello Mr. Doe” or “Hello, Mr. Doe”?

A. Commas should be used to set off words in what’s called “direct address”:

Thanks, Joe, I needed that.

That’s quite all right, Sarah. Everybody needs a large deep-dish pizza now and again.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]