Linking word

Hi everyone,

We say : "I don't know the answer, let alone he"
or " I can't swim let alone dive"

Q: Is it correct to use the subject pronoun "he" after "let alone"?
Q: Is "let alone" used ONLY in a negative sense?

What if we say: "John is smart. Jack is even smarter" (positive)

Q: Can we combine the two into: "John is smart, let alone Jack"?
or is it "John in smart and even more so is Jack" or "John is smart and Jack is even more so"?
Q: Is the phrase " even more so" used in a positive sense? THANKS