Looking at the OED, impression has always had the sense (since the late 1300s at least) of an imprint (such as an impression made in wax), and thus of a copy. That is precisely the Latin etymology. However, the word has also been used to describe the effect of something on the mind, which has come down to us in examples like "It gave me the impression that...", and "he made a good first impression". This, of course, comes from the idea that the thing or person is making a stamped image on the mind, which is a common trope in conceptions of consciousness (e.g. sense impressions).

Incidentally, the first usage of impression as a performance is listed as 1953. Interestingly, it is in scare quotes, but whether the OED has missed earlier usage I don't know.

Impersonation appears in 1825, and derives from an older sense which literally means to personify or render into a personality: thus, a soul is said to be "impersonated" when it is incarnated into a body (1633), or vices and passions are said to be "impersonated" when they are represented as human figures in literature (1790s). From the latter sense, it is an easy step to one person dramatically representing another, although when the faint air of deceit or counterfeit, as emphasised by Nah, Lance and John, began to cling to the word is unclear.

I use hyphens for multi-word adjectives beofre nouns:

"a once-in-a-lifetime experience"
"context-dependent behavior"

(Exception: don't put hyphens after -ly: "heavily guarded secret", but not "heavily-guarded secret")

I don't use them after nouns, though:

"behaviour is context dependent"

Clearly, the accepted norm for the pronounciation of aunt in the U.S. is "ant". And it's true, most people who would pronounce it "ont" usually say "ax" and generally speaking aren't the brightest folks.

Use double quotes for the outermost quotation. Then use single quotes for the inner quotation.

"David found a note that only had a few words written on it: 'I'm too tired to walk.'"

For a third level of nested quoting, alterante back to double quotes:

"David found a note that only had a few words written on it: 'I'm too "tired" to walk, if you know what I mean!'"

I would write: "four point nine seven five percent".

What does the firm you work for recommend as the accepted style?

The construction "All X are not Y" should be avoided because the meaning is unclear. Instead, it is better to say "Not all X are Y" or "No X are Y". Then the listener will understand.

Generations are discrete - there's no such thing as a "half generation".

If Shakespeare can say "God send every one their heart's desire", then so can I.

"You" as a singular was once mismatched in number, too, wasn't it? We've made it into a singular, though. If we did it with the second person, why is this not possible with the third?

"genius" is a noun.
"ingenious" is an adjective.

"-ous" is an English adjective ending; "-us" is a noun ending originating from Latin.

Consider the difference between "callus" and "callous".